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ELECTRIC  TRANSMISSION 

OF 

WATER  POWER 


By 
ALTON  D.  ADAMS,  A.M. 

MEMBER    AMERICAN    INSTITUTE    OF   ELECTRICAL    ENGINEERS 


NEW   YORK 

Me  GRAW-HILL    BOOK    Co. 
1906 


Copyrighted,  1906,  by  the 

McGRAW  PUBLISHING  COMPANY 

NEW  YORK 


TABLE   OF    CONTENTS 

CHAPTER  PAGE 

I.  WATER-POWER  IN  ELECTRICAL  SUPPLY i 

II.  UTILITY  OF  WATER-POWER  IN  ELECTRICAL  SUPPLY 10 

III.  COST  OF  CONDUCTORS  FOR  ELECTRIC-POWER  TRANSMISSION      .     .  19 

IV.  ADVANTAGES  OF  THE  CONTINUOUS  AND  ALTERNATING  CURRENT    .  31 
V.  THE  PHYSICAL  LIMITS  OF  ELECTRIC-POWER  TRANSMISSION        .    .  44 

VI.  DEVELOPMENT  OF  WATER-POWER  FOR  ELECTRIC  STATIONS    ...  51 

VII.  THE  LOCATION  OF  ELECTRIC  WATER-POWER  STATIONS      ....  64 

VIII.  DESIGN  OF  ELECTRIC  WATER-POWER  STATIONS 83 

IX.  ALTERNATORS  FOR  ELECTRICAL  TRANSMISSION 103 

X.  TRANSFORMERS  IN  TRANSMISSION  SYSTEMS 122 

XI.  SWITCHES,  FUSES,  AND  CIRCUIT -BREAKERS 135 

XII.  REGULATION  OF  TRANSMITTED  POWER 155 

XIII.  GUARD  WIRES  AND  LIGHTNING  ARRESTERS 168 

XIV.  ELECTRICAL  TRANSMISSION  UNDER  LAND  AND  WATER      ....  187 
XV.  MATERIALS  FOR  LINE  CONDUCTORS 200 

XVI.  VOLTAGE  AND  LOSSES  ON  TRANSMISSION  LINES 215 

XVII'.  SELECTION  OF  TRANSMISSION  CIRCUITS 233 

XVIII.  POLE  LINES  FOR  POWER  TRANSMISSION          246 

XIX.  ENTRIES  FOR  ELECTRIC  TRANSMISSION  LINES 261 

XX.  INSULATOR  PINS      .    .•    .*   . 270 

XXI.  INSULATORS  FOR  TRANSMISSION  LINES 287 

XXII.  DESIGN  OF  INSULATOR  PINS  FOR  TRANSMISSION  LINES    ....  298 

XXIII.  STEEL  TOWERS 306 


215144 


ELECTRIC  TRANSMISSION  OF  WATER- 
POWER. 

CHAPTER   I. 

WATER-POWER    IN    ELECTRICAL    SUPPLY. 

ELECTRICAL  supply  from  transmitted  water-power  is  now  distributed 
in  more  than  fifty  cities  of  North  America.  These  include  Mexico  City, 
with  a  population  of  402,000;  Buffalo  and  San  Francisco,  with  352,387 
and  342,782  respectively;  Montreal,  with  266,^26,  and  Los  Angeles,  St. 
Paul,  and  Minneapolis,  with  populations  that  range  between  100,000  and 
200,000  each.  North  and  south  these  cities  extend  from  Quebec  to  An- 
derson, and  from  Seattle  to  Mexico  City.  East  and  west  the  chain  of 
cities  includes  Portland,  Springfield,  Albany,  Buffalo,  Hamilton,  To- 
ronto, St.  Paul,  Butte,  Salt  Lake  City,  and  San  Francisco.  To  reach 
these  cities  the  water-power  is  electrically  transmitted,  in  many  cases 
dozens,  in  a  number  of  cases  scores,  and  in  one  case  more  than  two 
hundred  miles.  In  the  East,  Canada  is  the  site  of  the  longest  transmis- 
sion, that  from  Shawinigan  Falls  to  Montreal,  a  distance  of  eighty-five 
miles. 

From  Spier  Falls  to  Albany  the  electric  line  is  forty  miles  in  length. 
Hamilton  is  thirty-seven  miles  from  that  point  on  the  Niagara  escarp- 
ment, where  its  electric  power  is  developed.  Between  St.  Paul  and  its 
electric  water-power  station,  on  Apple  River,  the  transmission  line  is 
twenty-five  miles  long.  The  falls  of  the  Missouri  River  at  Canon  Ferry 
are  the  source  of  the  electrical  energy  distributed  in  Butte,  sixty-five  miles 
away.  Los  Angeles  draws  electrical  energy  from  a  plant  eighty-three 
miles  distant  on  the  Santa  Ana  River.  From  Colgate  power-house,  on 
the  Yuba,  to  San  Francisco,  by  way  of  Mission  San  Jose,  the  transmission 
line  has  a  length  of  220  miles.  Between  Electra  generating  station  in  the 
Sierra  Nevada  Mountains  and  San  Francisco  is  154  miles  by  the  electric 
line. 

These  transmissions  involve  large  powers  as  well  as  long  distances. 
The  new  plant  on  the  Androscoggin  is  designed  to  deliver  10,000  horse- 


ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


Fort  Ann 


Ashley  Falls 

Power 
Statio 


Greenwich 


Waterford 

Lansingburgh 

on 

Met 
Station 


ELECTRIC  RAILWAYS 
TRANSMISSION  LINES 

Scale  of  Miles 


10 


Remission  Lines. 


WATER-POWER  IN  ELECTRICAL  SUPPLY.  3 

power  for  electrical  supply  in  Lewiston,  Me.  At  Spier  Falls,  on  the 
Huason,  whence  energy  goes  to  Albany  and  other  cities,  the  electric  gen- 
erators will  have  a  capacity  of  32,000  horse-power.  From  the  two  water 
power  stations  at  Niagara  Falls,  with  their  twenty-one  electric  generators 
of  5, ooo. horse-power  each,  a  total  of  105,000,  more  than  30,000  horse- 
power is  regularly  transmitted  to  Buffalo  alone;  the  greater  part  of  the 
capacity  being  devoted  to  local,  industries.  Electrical  supply  in  St. 
Paul  is  drawn  from  a  water-power  plant  of  4,000  and  in  Minneapolis 
from  a  like  plant  of  7,400  horse-power  capacity.  The  Canon  Ferry  sta- 
tion, on  the  Missouri,  that  supplies  electrical  energy  in  both  Helena  and 
Butte,  has  a  capacity  of  10,000  horse-power.  Both  Seattle  and  Tacoma 
draw  electrical  supply  from  the  8,000  horse-power  plant  at  Snoqual- 
mie  Falls.  The  Colgate  power-house,  which  develops  energy  for  San 
Francisco  and  a  number  of  smaller  places,  has  electric  generators  of 
15,000  horse-power  aggregate  capacity.  At  the  Electra  generating  sta- 
tion, where  energy  is  also  transmitted  to  San  Francisco  and  other  cities 
on  the  way,  the  capacity  is  13,330  horse-power.  Electrical  supply  in 
Los  Angeles  is  drawn  from  the  generating  station  of  4,000  horse-power, 
on  the  Santa  Ana  River,  and  from  two  stations,  on  Mill  Creek,  with  an 
aggregate  of  4,600,  making  a  total  capacity  of  not  less  than  8,600  horse- 
power. Five  water-power  stations,  scattered  within  a  radius  of  ten  miles 
and  with  4,200  horse-power  total  capacity,  are  the  source  of  electrical 
supply  in  Mexico  City. 

The  foregoing  are  simply  a  part  of  the  more  striking  illustrations  of 
that  development  by  which  falling  water  is  generating  hundreds  of  thou- 
sands of  horse-power  for  electrical  supply  to  millions  of  population.  This 
application  of  great  water  powers  to  the  industrial  wants  of  distant  cities 
is  hardly  more  than  a  decade  old.  Ten  years  ago  Shawinigan  Falls  was 
an  almost  unheard-of  point  in  the  wilds  of  Canada.  Spier  Falls  was 
merely  a  place  of  scenic  interest;  the  Missouri  at  Canon  Ferry  was  not 
lighting  a  lamp  or  displacing  a  pound  of  coal ;  that  falling  water  in  the 
Sierra  Nevada  Mountains  should  light  the  streets  and  operate  electric  cars 
in  San  Francisco  seemed  impossible,  and  that  diversion  of  Niagara,  which 
seems  destined  to  develop  more  than  a  million  horse-power  and  leave 
dry  the  precipices  over  which  the  waters  now  plunge,  had  not  yet  begun. 
In  some  few  instances  where  water-power  was  located  in  towns  or  cities, 
it  has  been  applied  to  electrical  supply  since  the  early  days  of  the  indus- 
try. In  the  main,  however,  the  supply  of  electrical  energy  from  water- 
power  has  been  made  possible  only  by  long-distance  transmission.  The 
extending  radius  of  electrical  transmission  for  water-powers  has  formed 


4        ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


FIG.  2.— Snoqualmie  Falls  Transmission  Lines. 


WATER-POWER  IN  ELECTRICAL  SUPPLY.  5 

the  greatest  incentive  to  their  development.  This  development  in  turn 
has  reacted  on  the  conditions  that  limit  electrical  supply  and  has  mate- 
rially extended  the  field  of  its  application.  Transmitted  water-power  has 
reduced  the  rates  for  electric  service.  It  may  not  be  easy  to  prove  this 
reduction  by  quoting  figures  for  net  rates,  because  these  are  not  generally 
published,  but  there  are  other  means  of  reaching  the  conclusion. 

In  the  field  of  illumination  electricity  competes  directly  with  gas,  and 
in  the  field  of  motive  power  with  coal.  During  the  past  decade  it  is  well 
known  that  the  price  of  gas  has  materially  declined  and  the  price  of  coal, 
barring  the  recent  strike  period,  has  certainly  not  increased.  In  spite  of 
these  reductions  electrical  supply  from  water-power  has  displaced  both 
gas  and  coal  in  many  instances. 

Moreover,  the  expansion  of  electric  water-power  systems  has  been 
decidedly  greater,  as  a  rule,  than  that  of  electrical  supply  from  steam- 
driven  stations.  An  example  of  the  fact  last  stated  may  be  seen  in  Port- 
land, Me.  In  the  spring  of  1899,  a  company  was  formed  to  transmit  and 
distribute  electrical  energy  in  that  city  from  a  water-power  about  thirteen 
miles  distant.  For  some  years,  prior  to  and  since  the  date  just  named, 
an  extensive  electric  system  with  steam-power  equipment  has  existed  in 
Portland.  In  spite  of  this,  the  system  using  water-power,  on  January  i  st, 
1903,  had  a  connected  load  of  352  enclosed  arcs  and  20,000  incandescent 
lamps,  besides  835  horse-power  in  motors. 

Comparing  the  expansion  of  electric  water-power  systems  with  those 
operated  by  steam,  when  located  in  different  cities,  Hartford  and  Spring- 
field may  be  taken  on  the  one  hand  and  Fall  River  and  New  Bedford  on 
the  other.  The  use  of  water-power  in  electrical  supply  at  Hartford  be- 
gan in  November,  1891,  and  has  since  continued  to  an  increasing  extent. 
Throughout  the  same  period  electrical  supply  in  Fall  River  has  been 
derived  exclusively  from  steam.  In  1890  the  population  of  Hartford  was 
53,230,  and  in  1900  it  stood  at  79,850,  an  increase  of  50  per  cent.  At 
the  beginning  of  the  decade  Fall  River  had  a  population  of  74,398,  and 
at  its  close  the  figures  were  104, 863,  a  rise  of  40.9  per  cent.  In  1892  the 
connected  load  of  the  electric  supply  system  at  Fall  River  included  451 
arc  and  7,800  incandescent  lamps,  and  motors  aggregating  140  horse- 
power. By  1901  this  load  had  increased  to  1,111  arcs,  24,254  incandes- 
cent lamps,  and  600  horse-power  in  motors.  The  electric  supply  system 
at  Hartford  in  1892  was  serving  800  arcs,  2,000  incandescent  lamps,  and 
no  motors.  After  the  use  of  transmitted  water-power  during  nine  years 
the  connected  load  of  the  Hartford  system  had  come  to  include  1,679 
arcs,  68,725  incandescent  lamps,  and  3,476  horse-power  of  motor  capac- 


6         ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

ity  in  1901.  At  the  beginning  of  the  decade  Hartford  was  far  behind 
Fall  River  in  both  incandescent  lamps  and  motors,  but  at  the  end  Hart- 
ford had  nearly  three  times  as  many  incandescent  lamps  and  nearly  six 
times  as  great  a  capacity  in  connected  motors.  As  Fall  River  had  a  pop- 
ulation in  1900  that  was  greater  by  thirty-one  per  cent,  than  the  popula- 
tion of  Hartford,  and  the  percentage  of  increase  during  the  decade  was 
only  9.1  lower  in  the  former  city,  water-power  seems  to  have  been  the 
most  potent  factor  in  the  rise  of  electric  loads  in  the  latter.  Electric 
gains  at  Hartford  could  not  have  been  due  to  the  absence  of  competition 
by  gas,  for  the  price  of  gas  there  in  1901  was  $i  per  1,000  cubic  feet, 
while  the  price  in  Fall  River  was  $1.10  for  an  equal  amount. 

Water-power  began  to  be  used  in  electrical  supply  at  Springfield  dur- 
ing the  latter  half  of  1897.  ^n  that  year  the  connected  load  of  the  Spring- 
field electric  system  included  1,006  arcs,  24,778  incandescent  lamps,  and 
motors  with  a  capacity  of  647  horse-power.  Five  years  later,  in  1902, 
this  connected  load  had  risen  to  1,399  arc  lamps,  45,735  incandescent 
lamps,  and  a  capacity  of  1,025  horse-power  in  electric  motors.  At  New 
Bedford,  in  1897,  the  electric  system  was  supplying  406  arc  and  22,122 
incandescent  lamps  besides  motors  rated  at  298  horse-power.  This  load, 
in  1902,  had  changed  to  488  arcs,  18,055  incandescent  lamps,  and  432 
horse-power  in  capacity  of  electric  motors.  From  the  foregoing  figures 
it  appears  that  while  82  arc  lamps  were  added  in  New  Bedford, 
393  such  lamps  were  added  in  Springfield.  While  the  electric  load  at 
New  Bedford  was  increased  by  134  horse-power  of  motors,  the  like  in- 
crease at  Springfield  was  378  horse-power,  and  while  the  former  city  lost 
4,067  from  its  load  of  incandescent  lamps,  the  latter  gained  20,957  °^ 
these  lamps.  During  all  these  changes  electrical  supply  in  Springfield 
has  come  mostly  from  water-power,  and  that  in  New  Bedford  has  been 
the  product  of  steam.  Population  at  Springfield  numbered  44,179  in 
1890  and  62,059  in  1900,  an  increase  of  40.5  per  cent.  In  the  earlier  of 
these  years  New  Bedford  had  a  population  of  40,733,  and  in  the  later 
62,442,  an  increase  of  53.3  per  cent.  In  1902  the  average  price  obtained 
for  gas  at  Springfield  was  #1.04  and  at  New  Bedford  #1.18  per  1,000 
cubic  feet. 

Springfield  contains  a  prosperous  gas  system,  and  the  gross  income 
there  from  the  sale  of  gas  was  thirty-one,  per  cent  greater  in  1902  than 
in  1897.  During  this  same  period  of  five  years  the  gross  income  from 
sales  of  electrical  energy,  developed  in  large  part  by  water-power,  in- 
creased forty-seven  per  cent.  For  the  five  years  of  general  depression, 
ending  in  1897  tne  gross  annual  income  of  gas  sales  in  Springfield  rose 


WATER-POWER  IN  ELECTRICAL  SUPPLY.  7 

only  five  per  cent,  and  the  like  electric  income  nine  per  cent.  In  the  five 
years  last  named  the  electrical  supply  system  was  operated  with  coal. 

The  application  of  transmitted  water-power  in  electrical  supply  has 
displaced  steam  as  a  motive  power  in  many  large  industrial  plants  that 
never  would  have  been  operated  from  steam-driven  electric  stations.  An 
example  of  this  sort  exists  at  Portland,  where  one  of  the  motors  operated 
by  the  electric  water-power  system,  in  an  industrial  plant,  has  a  capacity 
of  300  horse-power.  Every  pound  of  coal  burned  in  Concord,  N.  H.,  is 
hauled  by  the  single  steam  railway  system  entering  that  city,  which  rail- 
way operates  large  car  and  repair  shops  there.  Some  years  ago  the  rail- 
way installed  a  complete  plant  of  engines,  dynamos,  and  motors  for  elec- 
tric-driving throughout  these  shops.  These  engines  and  dynamos  now 
stand  idle  and  the  motor  equipment,  with  an  aggregate  capacity  of  590 
horse-power,  is  operated  with  energy  purchased  from  the  local  electrical 
supply  system  and  drawn  from  water-power. 

Another  striking  example  of  the  ability  of  electric  water-power  systems 
to  make  power  rates  that  are  attractive  to  large  manufacturers  may  be 
seen  at  Manchester,  N.  H.  One  of  the  largest  manufacturing  plants  in 
that  city  purchases  energy  for  the  operation  of  the  equivalent  of  more  than 
7,000  incandescent  lamps,  and  of  motors  rated  at  976  horse-power,  from 
the  electrical  supply  system  there,  whose  generating  stations  are  driven 
mainly  by  water-power.  The  Manchester  electrical  supply  system  also 
furnishes  energy,  through  a  sub-station  of  8oo-horse-power  capacity,  to 
operate  an  electric  railway  connecting  Manchester  and  Concord.  This 
electric  line  is  owned  and  operated  in  common  with  the  only  steam  rail- 
way system  of  New  Hampshire,  so  that  the  only  inducement  to  purchase 
energy  from  the  water-power  system  seems  to  be  one  of  price. 

In  Buffalo  the  electric  transmission  system  from  Niagara  Falls 
supplies  large  motors  of  about  20,000  horse-power  capacity  in  manu- 
facturing and  industrial  works,  and  7,000  horse-power  to  the  street  rail- 
way system,  besides  another  4,000  horse-power  for  general  service  in 
lighting  and  small  motors.  Few  large  cities  in  the  United  States  have 
cheaper  coal  than  Buffalo,  and  in  Portland,  Concord,  and  Manchester 
coal  prices  are  moderate.  In  the  Rocky  Mountain  region,  where  coal  is 
more  expensive,  the  greater  part  of  the  loads  of  some  electric  water-power 
systems  is  made  up  of  large  industrial  works.  In  Salt  Lake  City  the  elec- 
trical supply  system,  which  draws  its  energy  almost  exclusively  from 
water-powers,  had  a  connected  load  of  motors  aggregating  2,600  horse- 
power as  far  back  as  1901,  and  also  furnished  energy  to  operate  the  local 
electric  railway,  and  several  smelters  six  miles  south  of  the  city,  besides 


8        ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


all  the  local  lighting  service.  As  good  lump  coal  sells  in  Salt  Lake  for 
#4.50  per  ton,  slack  at  less  than  one-half  this  figure,  and  the  population 
there  by  the  late  census  was  only  53,531 ,  the  figures  for  the  load  of  motors 
are  especially  notable.  At  Helena  energy  from  the  10,000  horse-power 
station  at  Canon  Ferry  operates  the  local  lighting  and  power  systems,  two 
smelting  and  a  mining  plant. 

In  Butte,  energy  from  the  station  just  named  operates  the  works  of 
five  smelting  and  mining  companies,  driving  motors  that  range  from  i  to 

CITIES  WITH  ELECTRICAL  SUPPLY  FROM  WATER-POWER. 


City. 

Miles  from  Water- 
Power  to  City. 

Horse-Power  of 
Water-  Driven 
Stations. 

Population. 

Mexico  City  

I  O  to  I  ^ 

4  200 

402  ooo 

Buffalo  

2  3 

#2Q  OOO 

•2IT2    387 

Montreal  . 

8? 

266,826 

San  Francisco  

147 

I  3  3  30 

742,782 

Minneapolis 

2O2  7l8 

St  Paul  . 

2? 

4  ooo 

163  o6"\ 

Los  Angeles. 

8* 

8  600 

IO2  47O 

Albany.  .  . 

°o 

4.O 

32  ooo 

O4  I  ^1 

Portland,  Ore.   . 

oo  426 

Hartford  

I  j 

3600 

70  8<;o 

Springfield,  Mass  

6 

3  780 

62  o^o 

Manchester  N  H 

T  2       £ 

CQ   08? 

Salt  Lake  City  

16'5 
26  c 

>6/<J 
IO  OOO 

C7,C^I 

Portland  Me 

1  3. 

2  660 

CQ  14? 

Seattle 

xo 

8  ooo 

80  671 

Butte 

fc 

IO  OOO 

3O  47O 

Oakland 

14.2 

je  OOO 

66.OOO 

3- 

•I  OOO 

22,76l 

Concord  N.  H  

4" 

I  OOO 

10,63,2 

Helena,  Mont  

2O 

IO,77O 

Hamilton  Ont 

2C 

8  ooo 

Quebec  

7 

3,000 

Dales  Ore 

27 

I   33O 

*  Power  received. 

800  horse-power  in  individual  capacity.    The  capacity  of  the  Butte  sub- 
station is  7,600  horse-power. 

The  great  electric  water  power  system  marked  by  the  Santa  Ana  sta- 
tion at  one  end  and  the  city  of  Los  Angeles  at  the  other,  eighty-three  miles 
distant,  includes  more  than  160  miles  of  transmission  lines,  several  hun- 
dred miles  of  distribution  circuits,  and  supplies  light  and  power  in  twelve 
cities  and  towns.  Among  the  customers  of  this  system  are  an  electric 
railway,  a  number  of  irrigation  plants,  and  a  cement  works.  These 


WATER-POWER  IN  ELECTRICAL  SUPPLY.  9 

works  contain  motors  that  range  from  10  to  200  horse-power  each  in 
capacity.  Motors  of  fifty  horse-power  or  less  are  used  at  pumping  sta- 
tions in  the  irrigation  systems. 

Applications  of  water-power  in  electrical  supply  during  the  past  de- 
cade have  prepared  the  way  for  a  much  greater  movement  in  this  direc- 
tion. Work  is  now  under  way  for  the  electric  transmission  of  water- 
power,  either  for  the  first  time  or  in  larger  amounts,  to  Albany,  Toronto, 
Chicago,  Duluth,  Portland,  Oregon,  San  Francisco,  Los  Angeles,  and 
dozens  of  other  cities  that  might  be  named. 

Another  ten  years  will  see  the  greater  part  of  electrical  supply  on  the 
American  continent  drawn  from  water-power. 

Only  the  largest  city  supplied  from  each  water-power  is  named  above. 
Thus  the  same  transmission  system  enters  Albany,  Troy,  Schenectady. 
Saratoga,  and  a  number  of  smaller  places. 


CHAPTER  II. 

UTILITY   OF    WATER-POWER   IN    ELECTRICAL    SUPPLY. 

IN  comparatively  few  systems  is  the  available  water-power  sufficient 
to  carry  the  entire  load  at  all  hours  of  the  day,  and  during  all  months  of 
the  year,  so  that  the  question  of  how  much  fuel  can  be  saved  is  an  un- 
certain one  for  many  plants.  Again,  the  development  of  water-power 
often  involves  a  large  investment,  and  may  bring  a  burden  of  fixed 
charges  greater  than  the  value  of  the  fuel  saved. 

In  spite  of  these  conflicting  opinions  and  factors,  the  application  of 
water-power  in  electrical  systems  is  now  going  on  faster  than  ever  before. 
If  a  saving  of  fuel,  measured  by  the  available  flow  of  water  during  those 
hours  when  it  can  be  devoted  directly  to  electrical  supply,  were  its  only 
advantage,  the  number  of  cases  in  which  this  power  could  be  utilized  at  a 
profit  would  be  relatively  small.  If,  on  the  other  hand,  all  of  the  water 
that  passes  down  a  stream  could  be  made  to  do  electrical  work,  and  if  the 
utilization  of  this  water  had  other  advantages  nearly  or  quite  as  great  as 
the  reduction  of  expense  for  coal,  then  many  water-powers  would  await 
only  development  to  bring  profit  to  their  owners. 

No  part  of  the  problem  is  more  uncertain  than  the  first  cost  and  sub- 
sequent fixed  charges  connected  with  the  development  of  water-power. 
To  bring  out  the  real  conditions,  the  detailed  facts  as  to  one  or  more 
plants  may  be  of  greater  value  than  mere  general  statements  covering 
a  wide  range  of  cases. 

On  a  certain  small  river  the  entire  water  privilege  at  a  point  where  a 
fall  of  fourteen  feet  could  be  made  available  was  obtained  several  years 
ago.  At  this  point  a  substantial  stone  and  concrete  dam  was  built,  and 
also  a  stone  and  brick  power-house  with  concrete  floor  and  steel  truss 
roof.  In  this  power-house  were  installed  electric  generators  of  800  kilo- 
watts total  capacity,  direct-connected  to  horizontal  turbine  wheels.  The 
entire  cost  of  the  real  estate  necessary  to  secure  the  water-power  privilege 
plus  the  cost  of  all  the  improvements  was  about  #130,000.  More  than 
enough  water-power  to  drive  the  8oo-kilowatt  generators  at  full  load  was 
estimated  to  be  available,  except  at  times  of  exceptionally  low  water.  At 
this  plant  the  investment  for  the  water-power  site,  development,  and 


UTILITY  OF  WATER-POWER.  n 

complete  equipment  was  thus  #162  per  kilowatt  capacity  of  generators 
installed. 

Allowing  6 5  days  of  low  water,  these  generators  of  800  kilowatts  capac- 
ity may  be  operated  300  days  per  year.  If  the  running  time  averages 
ten  hours  daily  at  full  load,  the  energy  delivered  per  year  is  2,400,000 
kilowatt  hours.  Ten  per  cent  of  the  total  investment  should  be  ample 
to  cover  interest  and  depreciation  charges,  and  this  amounts  to  $13,000 
yearly.  It  follows  that  the  items  of  interest  and  depreciation  on  the 
original  investment  represent  a  charge  of  0.54  cent  per  kilowatt  hour  on 
the  assumed  energy  output  at  this  plant.  This  energy  is  transmitted  a 
few  miles  and  used  in  the  electrical  supply  system  of  a  large  city. 

On  another  river  the  entire  water  privilege  was  secured  about  four 
years  ago  at  a  point  where  a  fall  of  more  than  20  feet  between  ledges  of 
rock  could  be  obtained  and  more  than  2,000  horse-power  could  be  devel- 
oped. At  this  point  a  masonry  dam  and  brick  power-house  were  built, 
and  horizontal  turbine  wheels  were  installed,  direct-connected  to  electric 
generators  of  1,500  kilowatts  total  capacity.  The  entire  cost  of  real  es- 
tate, water  rights,  dam,  building,  and  equipment  in  this  case  was  about 
$250,000. 

Assuming,  as  before,  that  generators  may  be  operated  at  full  capacity 
for  10  hours  per  day  during  300  days  per  year,  the  energy  delivered  by 
this  plant  amounts  to  4,500,000  kilowatt  hours  yearly.  The  allowance 
of  10  per  cent  on  the  entire  investment  for  interest  and  depreciation  is 
represented  by  $25,000  yearly  in  this  case,  or  0.56  cent  per  kilowatt  hour 
of  probable  output.  Energy  from  this  plant  is  transmitted  and  used  in 
a  large  system  of  electrical  supply. 

If,  through  lack  of  water  or  inability  to  store  water  or  energy  at  times 
when  it  is  not  wanted,  generators  cannot  be  operated  at  full  capacity 
during  the  average  number  of  hours  assumed  above,  the  item  of  interest 
and  depreciation  per  unit  of  delivered  energy  must  be  higher  than  that 
computed.  With  the  possible  figure  for  this  item  at  less  than  six- 
tenths  of  a  cent  per  kilowatt  hour,  there  is  opportunity  for  some  in- 
crease before  it  becomes  prohibitive.  At  the  plant  last  named  the  entire 
investment  amounted  to  $166  per  kilowatt  capacity  of  connected  genera- 
tors, compared  with  $162  in  the  former  case,  and  these  figures  may  be 
taken  as  fairly  representative  for  the  development  of  water-power  in  a 
first-class  manner  on  small  rivers,  under  favorable  conditions.  In  both 
of  these  instances  the  power-houses  are  quite  close  to  the  dams.  If  long 
canals  or  pipe  lines  must  be  built  to  convey  the  water,  the  expense  of 
development  may  be  greatly  increased. 


12       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

One  advantage  of  water-  over  steam-power  is  the  smaller  cost  of  the 
building  with  the  former  for  a  given  capacity  of  plant.  The  building  for 
direct-connected  electric  generators,  driven  by  water-wheels,  is  relatively 
small  and  simple.  Space  for  fuel,  boilers,  economizers,  feed-water  heat- 
ers, condensers,  steam  piping,  and  pumps  is  not  required  where  water- 
power  is  used.  No  chimney  or  apparatus  for  mechanical  draught  is 
needed. 

The  model  electric  station  operated  by  water-power  usually  consists 
of  a  single  room  wLh  no  basement  under  it.  One  such  station  has  floor 
dimensions  27  by  52  feet,  giving  an  area  of  1,404  square  feet,  and  contains 
generators  of  800  kilowatts  capacity.  This  gives  1.75  square  feet  of  floor 
space  per  kilowatt  of  generators.  In  this  station  there  is  ample  room  for 
all  purposes,  including  erection  or  removal  of  machinery. 

Next  to  the  saving  of  fuel,  the  greatest  advantage  of  water-power  is 
due  to  the  relatively  small  requirements  for  labor  at  generating  stations 
where  it  is  used.  This  is  well  illustrated  by  an  example  from  actual 
practice.  In  a  modern  water-power  station  that  contributes  to  electrical 
supply  in  a  large  city  the  generator  capacity  is  1,200  kilowatts.  All  of 
the  labor  connected  with  the  operation  of  this  station  during  nearly 
twenty-four  hours  per  day  is  done  by  two  attendants  working  alternate 
shifts. 

These  attendants  live  close  to  the  station  in  a  house  owned  by  the 
electric  company,  and  receive  #60  each  per  month  in  addition  to  house 
rent.  Considering  the  location,  #i  2  per  month  is  probably  ample  allow- 
ance for  the  rent.  This  brings  the  total  expense  of  operation  at  this 
station  for  labor  up  to  #132  per  month,  or  #1,584  per  year,  a  sum  corre- 
sponding to  #1.32  yearly  per  kilowatt  of  generator  capacity. 

At  steam-power  stations  of  about  the  above  capacity,  operating 
twenty-four  hours  daily,  $6  is  an  approximate  yearly  cost  of  labor  per 
kilowatt  of  generators  in  use.  It  thus  appears  that  water-power  plants 
may  be  operated  at  less  than  one-fourth  of  the  labor  expense  necessary 
at  steam  stations  per  unit  of  capacity.  On  an  average,  the  combined 
cost  of  fuel  and  labor  at  electric  stations  driven  by  steam-power  is  a  little 
more  than  76  per  cent  of  their  total  cost  of  operation.  Of  this  total,  labor 
represents  about  28,  and  fuel  about  48  per  cent.  Water-power,  by  dis- 
pensing with  fuel  and  with  three-fourths  of  the  labor  charge,  reduces  the 
expense  of  operation  at  electric  stations  by  fully  69  per  cent. 

But  this  great  saving  in  the  operating  expenses  of  electric  stations  can 
be  made  only  where  water  entirely  displaces  coal.  If  part  water-power 
and  part  coal  are  used,  the  result  depends  on  the  proportion  of  each,  and 


i  UTILITY  OF  WATER-POWER.  13 

is  obviously  much  affected  by  the  variations  of  water-power  capacity. 
In  such  a  mixed  system  the  saving  effected  by  water-power  must  also 
depend  on  the  extent  to  which  its  energy  can  be  absorbed  at  all  hours  of 

Jan.    Feb.   Mar.  April  May    June  July   A"ug.  Sept.  Oct.  Nov.   Dec., 
100 


10      12      2       4       6       8       10      12 


A.M. 
ENERGY  CURVES  FROM!  WATER  POWER  ELECTRIC  STATIONS; 

FIG.  3. 

the  day.  By  far  the  greater  number  of  electric  stations  using  water- 
power  are  obliged  also  to  employ  steam  during  either  some  months  in 
the  year  or  some  hours  in  the  day,  or  both. 

It  is  highly  important,  therefore,  to  determine,  as  nearly  as  may  be, 
the  answers  to  three  questions: 


i4       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

First,  what  variations  are  to  be  expected  in  the  capacity  of  a  water- 
power  during  the  several  months  of  a  year  ? 

Second,  if  the  daily  flow  of  water  is  equal  in  capacity  to  the  daily  out- 
put of  electrical  energy,  how  far  can  the  water-power  be  devoted  to  the 
development  of  that  energy  ? 

Third,  with  a  water-power  sufficient  to  carry  all  electrical  loads  at 
times  of  moderately  high  water,  what  percentage  of  the  yearly  output  of 
energy  in  a  general  supply  system  can  be  derived  from  the  water  ? 

To  the  first  of  these  questions  experience  alone  can  furnish  an  answer. 
Variations  in  the  discharge  of  rivers  during  the  different  months  of  a  year 
are  very  great.  In  a  plant  laid  out  with  good  engineering  skill  some  pro- 
vision will  be  made  for  the  storage  of  water,  and  the  capacity  of  generat- 
ing equipment  will  correspond  to  some  point  between  the  highest  and 
lowest  rates  of  discharge. 

Curve  No.  i  in  the  diagram  on  the  opposite  page  represents  the  energy 
output  at  an  electric  station  driven  entirely  by  water-power  from  a  small 
stream  during  the  twelve  months  of  1901,  the  entire  flow  of  the  stream 
being  utilized.  During  December,  1901,  the  output  of  this  station  was 
527,700  kilowatts,  and  was  greater  than  that  in  any  other  month  of  the 
year.  Taking  this  output  at  100  per  cent,  the  curve  is  platted  to  show 
the  percentage  attained  by  the  delivered  energy  in  each  of  the  other  months. 
At  the  lowest  point  on  the  curve,  corresponding  to  the  month  of  February, 
the  output  of  energy  was  only  slightly  over  33  per  cent  of  that  in  De- 
cember. During  nine  other  months  of  the  year  the  proportion  of  energy 
output  to  that  in  December  was  over  60  and  in  three  months  over  80  per 
cent.  For  the  twelve  months  the  average  delivery  of  energy  per  month 
was  73.7  per  cent  of  that  during  December. 

PERCENTAGES  OF  ENERGY  DELIVERED  IN  DIFFERENT  MONTHS,  1901. 

January 68.0  May 77-9  September 79.3 

February 33.1  June 58.6  October 65.9 

March 80.5  Juty 67.7  Novermbe 95-8 

April 81.7  August 75-8  December 100.0 

At  a  somewhat  small  water-power  station  on  another  river  with  a 
watershed  less  precipitous  than  that  of  the  stream  just  considered,  the 
following  results  were  obtained  during  the  twelve  months  ending  June 
3oth,  1900.  For  this  plant  the  largest  monthly  output  of  energy  was  in 
November,  and  this  output  is  taken  at  100  per  cent.  The  smallest  de- 
livery of  energy  was  in  October,  when  the  percentage  was  53.1  of  the 
amount  for  November.  In  each  of  seven  other  months  of  the  year  the 
output  of  energy  was  above  80  per  cent  of  that  in  November.  During 


UTILITY  OF  WATER-POWER.  15 

March,  April,  May,  and  June  the  water-power  yielded  all  of  the  energy 
required  in  the  electrical  supply  system  with  which  it  was  connected,  and 
could,  no  doubt,  have  done  more  work  if  necessary.  For  the  twelve 
months  the  average  delivery  of  energy  per  month  was  80.6  per  cent  of 
that  in  November,  the  month  of  greatest  output. 

PERCENTAGES  OF  ENERGY  DELIVERED  IN  DIFFERENT  MONTHS,    1899  AND    1900. 

July 68.6  November 100.0  March 98.5 

August 69.1  December 87.0  April 85.7 

September 73-3  January 84.9  May 80.8 

October 53.1  February 9J-3  June 74.9 

The  gentler  slopes  and  better  storage  facilities  of  this  second  river 
show  their  effect  in  an  average  monthly  delivery  of  energy  6.9  per  cent 
higher  as  to  the  output  in  a  month  when  it  was  greatest  than  the  like  per- 
centage for  the  water-power  first  considered.  These  two  water-power 
illustrate  what  can  be  done  with  only  very  moderate  storage  capacities 
on  the  rivers  involved.  At  both  stations  much  water  escapes  over  the 
dams  during  several  months  of  each  year.  With  enough  storage  space 
to  retain  all  waters  of  these  rivers  until  wanted  the  energy  outputs  could 
be  largely  increased. 

As  may  be  seen  by  inspection  of  curve  No.  2,  the  second  water-power 
has  smaller  fluctuations  of  capacity,  as  well  as  a  higher  average  percent- 
age of  the  maximum  output  than  the  water-power  illustrated  by  curve 
No.  i. 

If  the  discharge  of  a  stream  during  each  twenty-four  hours  is  just 
sufficient  to  develop  the  electrical  energy  required  in  a  supply  system  dur- 
ing that  time,  the  water  may  be  made  to  do  all  of  the  electrical  work  in 
one  of  two  ways.  If  the  water-power  has  enough  storage  capacity  be- 
hind it  to  hold  the  excess  of  water  during  some  hours  of  the  day,  then  it 
is  only  necessary  to  install  enough  water-wheels  and  electric  generators 
to  carry  the  maximum  load.  Should  the  storage  capacity  for  water  be 
lacking,  or  the  equipment  of  generating  apparatus  be  insufficient  to  work 
at  the  maximum  rate  demanded  by  the  electrical  system,  then  an  electric 
storage  battery  must  be  employed  if  all  of  the  water  is  to  be  utilized  and 
made  to  do  the  electrical  work. 

The  greatest  fluctuations  between  maximum  and  minimum  daily 
loads  at  electric  lighting  stations  usually  occur  in  December  and  January. 
The  extent  of  these  fluctuations  is  illustrated  by  curve  No.  3,  which  rep- 
resents the  total  load  on  a  large  electrical  supply  system  during  a  typical 
week-day  of  January,  1901.  On  this  day  the  maximum  load  was  2,720 
and  the  minimum  load  612  kilowatts,  or  22.5  per  cent  of  the  highest  rate 


16       ELECTRIC  TRANSMISSION  OF  WATER-POWER 

of  output.  During  the  day  in  question  the  total  delivery  of  energy  for 
the  twenty-four  hours  was  30,249  kilowatt  hours,  so  that  the  average  load 
per  hour  was  1,260  kilowatts.  This  average  is  46  per  cent  of  the  maxi- 
mum load. 

Computation  of  the  area  included  by  curve  No.  3  above  the  average 
load  line  of  1,260  kilowatts  shows  that  about  17.8  per  cent  of  the  total 
output  of  energy  for  the  day  was  delivered  above  the  average  load,  that 
is,  in  addition  to  an  output  at  average  load.  It  further  appears  by  in- 
spection of  this  load  curve  that  this  delivery  of  energy  above  the  average 
load  line  took  place  during  12.3  hours  of  the  day,  so  that  its  average  rate 
of  delivery  per  hour  was  438  kilowatts. 

If  a  water-power  competent  to  carry  a  load  of  1,260  kilowatts  twenty- 
four  hours  per  day  be  applied  to  the  system  illustrated  by  curve  No.  3, 
then  about  17.8  per  cent  of  the  energy  of  the  water  for  the  entire  day 
must  be  stored  during  11.7  hours  and  liberated  in  the  remaining  12.3 
hours.  This  percentage  of  the  total  daily  energy  of  the  water  amounts 
to  36  per  cent  of  its  energy  during  the  hours  that  storage  takes  place. 

If  all  of  the  storage  is  done  with  water,  the  electric  generators  must 
be  able  to  work  at  the  rate  of  2,720  kilowatts,  the  maximum  load.  If  all 
of  the  storage  is  done  in  electric  batteries,  the  use  of  water  may  be  uni- 
form throughout  the  day,  and  the  generator  capacity  must  be  enough 
above  i, 260  kilowatts  to  make  up  for  losses  in  the  batteries.  Where 
batteries  are  employed  the  amount  of  water  will  be  somewhat  greater 
.  than  that  necessary  to  operate  the  load  directly  with  generators,  because 
of  the  battery  losses. 

In  spite  of  the  large  fluctuations  of  electrical  loads  throughout  each 
twenty-four  hours,  it  is  thus  comparatively  easy  to  operate  them  with 
water-powrers  that  are  little,  if  any,  above  the  requirements  of  the  average 
loads. 

Perhaps  the  most  important  question  relating  to  the  use  of  water- 
power  in  electrical  supply  is  what  percentage  of  the  yearly  output  of 
energy  can  be  derived  from  water  where  this  power  is  sufficient  to  carry 
the  entire  load  during  a  part  of  the  year.  With  storage  area  for  all  sur- 
plus water  in  any  season,  the  amount  of  work  that  could  be  done  by  a 
stream  might  be  calculated  directly  from  the  records  of  its  annual  dis- 
charge of  water.  As  such  storage  areas  for  surplus  water  have  seldom, 
or  never,  been  made  available  in  connection  with  electrical  systems,  the 
best  assurance  as  to  the  percentage  of  yearly  output  that  may  be  derived 
from  water-power  is  found  in  the  experience  of  existing  plants. 

The  question  now  to  be  considered  differs  materially  from  that  in- 


UTILITY  OF  WATER-POWER.  17 

volving  merely  the  variations  of  water-power  in  the  several  months,  or 
even  the  possible  yearly  output  from  water-power.  The  ratio  of  output 
from  water-power  to  the  total  yearly  output  of  an  electrical  system  in- 
cludes the  result  of  load  fluctuations  in  every  twenty-four  hours  and  the 
variable  demands  for  electrical  energy  in  different  months,  as  well  as 
changes  in  the  amount  of  water-power  available  through  the  seasons. 

In  order  to  show  the  combined  result  of  these  three  important  factors 
curve  No.  4  has  been  constructed.  This  indicates  the  percentages  of 
total  semi-yearly  outputs  of  electrical  energy  derived  from  water-power 
in  two  supply  systems.  Each  half-year  extends  either  from  January  to 
June,,  inclusive,  or  from  July  to  December,  inclusive,  and  thus  covers  a 
wet  and  dry  season.  Each  half-year  also  includes  a  period  of  maximum 
and  one  of  minimum  demand  for  electrical  energy  in  lighting.  The  pe- 
riod of  largest  water  supply  usually  nearly  coincides  with  that  of  heaviest 
lighting  load,  but  this  is  not  always  true. 

Electrical  systems  have  purposely  been  selected  in  which  the  water- 
power  in  at  least  one  month  of  each  half-year  was  nearly  or  quite  suf- 
ficient to  carry  the  entire  electrical  load.  The  percentage  of  energy 
from  water-power  to  the  total  energy  delivered  by  the  system  is  presented 
for  each  of  five  half-years.  Three  of  the  half-years  each  run  from  July 
to  December,  and  two  extend  from  January  to  June,  respectively.  The 
half  years  that  show  percentages  of  66.8,  80.2,  and  95.6,  respectively,  for 
the  relation  of  energy  from  water-power  to  the  total  electrical  output 
relate  to  one  system,  and  the  half  years  that  show  percentages  of  81.97 
and  94.3  for  the  energy  from  water-power  relate  to  another  system. 

For  the  half-year  when  66.8  per  cent,  of  the  output  of  the  electrical 
system  was  derived  from  water-power,  the  total  output  of  the  system  was 
3,966,026  kilowatt  hours.  During  the  month  of  December  in  this  half- 
year  more  than  98  per  cent  of  the  electrical  energy  delivered  by  the 
system  was  from  water-power,  though  the  average  for  the  six  months  was 
only  66.8  per  cent  from  water. 

In  the  following  six  months,  from  January  to  June,  the  electrical  sup- 
ply system  delivered  4,161,754  kilowatt  hours,  and  of  this  amount  the 
water-power  furnished  80.2  per  cent.  For  the  six  months  just  named, 
one  month,  May,  saw  99  per  cent  of  all  the  delivered  energy  derived  from 
water-power. 

The  same  system  during  the  next  half-year,  from  July  to  December, 
without  any  addition  to  its  water-power  development  or  equipment,  got 
95.6  per  cent  of  its  entire  energy  output  from  water-power,  and  this  out- 
put amounted  to  4,41 5,945  kilowatt  hours.  In  one  month  of  the  half- 


i8      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

year  just  named  only  0.2  per  cent  of  the  output  was  generated  with 
steam-power. 

These  three  successive  half  years  illustrate  the  fluctuations  of  the 
ratio  between  water-power  outputs  and  the  demands  for  energy  on  a 
single  system  of  electrical  supply.  The  percentage  of  81.9  for  energy 
derived  from  water-power  during  the  half-year  from  July  to  December 
represents  the  ratio  of  output  from  water  to  the  total  for  an  electrical  sup- 
ply system  where  water  generated  94  per  cent  of  all  the  energy  delivered 
in  one  month. 

In  the  same  system  during  the  following  six  months,  with  exactly  the 
same  water-power  equipment,  the  percentage  of  output  from  water-power 
was  94.3  of  the  total  kilowatt-hours  delivered  by  the  system.  This  result 
was  reached  in  spite  of  the  fact  that  the  total  outputs  of  the  system  in  the 
two  half-years  were  equal  to  within  less  than  one  per  cent. 

The  lesson  from  the  record  of  these  five  half-years  is  that  compara- 
tively large  variations  are  to  be  expected  in  the  percentage  of  energy  de- 
veloped by  water-power  to  the  total  output  of  electrical  supply  systems 
in  different  half-years.  But,  in  spite  of  these  variations,  the  portion  of 
electrical  loads  that  may  be  carried  by  water-power  is  sufficient  to  war- 
rant its  rapidly  extending  application  to  lighting  and  power  in  cities  and 
towns. 


CHAPTER  III. 

COST  OF  CONDUCTORS  FOR  ELECTRIC-POWER  TRANSMISSION. 

ELECTRICAL  transmission  of  energy  involves  problems  quite  distinct 
from  its  development.  A  great  water-power,  or  a  location  where  fuel 
is  cheap,  may  offer  opportunity  to  generate  electrical  energy  at  an  excep- 
tionally low  cost.  This  energy  may  be  used  so  close  to  the  point  of  its 
development  that  the  cost  of  transmission  is  too  small  for  separate  con- 
sideration. 

An  example  of  conditions  where  the  important  problems  of  transmis- 
sion are  absent  exists  in  the  numerous  factories  grouped  about  the  great 
water-power  plants  at  Niagara  and  drawing  electrical  energy  from  it.  In 
such  a  case  energy  flows  directly  from  the  dynamos,  driven  by  water- 
power,  to  the  lamps,  motors,  chemical  vats,  and  electric  heaters  of  con- 
sumers through  the  medium,  perhaps,  of  local  transformers.  Here  the 
costs  and  losses  of  transmitting  or  distributing  equipments  are  minor 
matters,  compared  with  the  development  of  the  energy. 

If,  now,  energy  from  the  water-power  is  to  be  transmitted  over  a  dis- 
tance of  many  miles,  a  new  set  of  costs  is  to  be  met.  In  the  first  place, 
it  will  be  necessary  to  raise  the  voltage  of  the  transmitted  energy  much 
above  the  pressure  at  the  dynamos  in  order  to  save  in  the  weight  and  cost 
of  conductors  for  the  transmission  line.  This  increase  of  voltage  requires 
transformers  with  capacity  equal  to  the  maximum  rate  at  which  energy 
is  to  be  delivered  to  the  line.  These  transformers  will  add  to  the  cost  of 
the  energy  that  they  deliver  in  two  ways :  by  the  absorption  of  some  energy 
to  form  heat,  and  by  the  sum  of  annual  interest,  maintenance,  and  depre- 
ciation charges  on  the  price  paid  for  them.  Other  additions  to  the  cost 
of  energy  delivered  by  the  transmission  line  must  be  made  to  cover  the 
annual  interest,  maintenance,  and  depreciation  charges  on  the  amount  of 
the  line  investment,  and  to  pay  for  the  energy  changed  to  heat  in  the 
line. 

Near  the  points  where  the  energy  is  to  be  used,  the  transmission  line 
must  end  in  transformers  to  reduce  the  voltage  to  a  safe  figure  for  local 
distribution.  This  second  set  of  transformers  will  further  add  to  the 
cost  of  the  delivered  energy  in  the  same  ways  as  the  former  set. 

19 


20      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

From  these  facts  it  is  evident  that,  to  warrant  an  electrical  transmis- 
sion, the  value  of  energy  at  the  point  of  distribution  should  at  least  equal 
the  value  at  the  generating  plant  plus  the  cost  of  the  transmission. 
Knowing  the  cost  of  energy  at  one  end  of  the  transmission  line  and  its 
value  at  the  other,  the  difference  between  these  two  represents  the  maxi- 
•mum  cost  at  which  the  transmission  will  pay. 

Three  main  factors  are  concerned  in  the  cost  of  electric  power  trans- 
mission, namely,  the  transformers,  the  pole  line,  and  the  wire  or  con- 
ductors. These  factors  enter  into  the  cost  of  transmitted  energy  in  very 
different  degrees,  according  to  the  circumstances  of  each  case.  The 
maximum  and  average  rates  of  energy  transmission,  the  total  voltage, 
the  percentage  of  line  loss,  and  the  length  of  the  line  mainly  determine 
the  relative  importance  of  the  transformers,  pole  line,  and  conductors  in 
the  total  cost  of  delivered  energy. 

First  cost  of  transformers  varies  directly  with  the  maximum  rate  of 
transmission,  and  is  nearly  independent  of  the  voltage,  the  length  of  the 
transmission,  and  the  percentage  of  line  loss.  A  pole  line  changes  in  first 
cost  with  the  length  of  the  transmission,  but  is  nearly  independent  of  the 
other  factors.  Line  conductors,  for  a  fixed  maximum  percentage  of  loss, 
vary  in  first  cost  directly  with  the  square  of  the  length  of  the  transmission 
and  with  the  rate  of  the  transmission ;  but  their  first  cost  decreases  as  the 
percentage  of  line  loss  increases  and  as  the  square  of  the  voltage  of  trans- 
mission increases. 

If  a  given  amount  of  power  is  to  be  transmitted,  at  a  certain  percent- 
age of  loss  in  the  line  and  at  a  fixed  voltage,  over  distances  of  50, 100,  and 
200  miles,  respectively,  the  foregoing  principles  lead  to  the  following  con- 
clusions :  The  capacity  of  transformers  being,  fixed  by  the  rate  of  trans- 
mission, will  be  the  same  for  either  distance,  and  their  cost  is  therefore 
constant.  Transformer  losses,  interest,  depreciation,  and  repairs  are  also 
constant.  The  cost  of  pole  line,  depending  on  its  length,  will  be  twice  as 
great  at  100  and  four  times  as  great  at  200  as  at  50  miles.  Interest,  depre- 
ciation, and  repairs  will  also  go  up  directly  with  the  length  of  the  pole  lines. 

Line  conductors  will  cost  four  times  as  much  for  the  loo-as  for  the 
50-mile  transmission,  because  their  weight  will  be  four  times  as  great,and 
the  annual  interest  and  depreciation  will  go  up  at  the  same  rate.  For  the 
transmission  of  200  miles  the  cost  of  line  conductors  and  their  weight  will 
be  sixteen  times  as  great  as  the  cost  at  50  miles.  It  follows  that  interest, 
depreciation,  and  maintenance  will  be  increased  sixteen  times  with  the 
2oo-mile  transmission  over  what  they  were  at  50  miles,  if  voltage  and  line 
loss  are  constant. 


COST  OF  CONDUCTORS  FOR  TRANSMISSION.       21 

A  concrete  example  of  the  cost  of  electric  power  transmission  over  a 
given  distance  will  illustrate  the  practical  application  of  these  principles. 
Let  the  problem  be  to  deliver  electrical  energy  in  a  city  distant  100  miles 
from  the  generating  plant !  Transformers  with  approximately  twice  the 
capacity  corresponding  to  the  maximum  rate  of  transmission  must  be 
provided,  because  one  set  is  required  at  the  generating  and  another  at  the 
delivery  station.  The  cost  of  these  transformers  will  be  approximately 
$7.50  per  horse-power  for  any  large  capacity. 

Reliability  is  of  the  utmost  importance  in  a  great  power  transmission, 
and  this  requires  a  pole  line  of  the  most  substantial  construction.  Such 
a  line  in  a  locality  where  wooden  poles  can  be  had  at  a  moderate  price 
will  cost,  with  conductors  in  position,  about  $700  per  mile,  exclusive  of 
the  cost  of  the  conductors  themselves  or  of  the  right  of  way  but  in- 
cluding the  cost  of  erecting  the  conductors.  The  100  miles  of  pole 
line  in  the  present  case  should,  therefore,  be  set  down  at  a  cost  of 
$70,000. 

A  large  delivery  of  power  must  be  made  to  warrant  the  construction 
of  so  long  and  expensive  a  line,  and  10,000  horse-power  may  be  taken  as 
the  maximum  rate  of  delivery.  On  the  basis  of  two  horse-power  of 
transformer  capacity  for  each  horse-power  of  the  maximum  delivery  rate, 
transformers  with  a  capacity  of  20,000  horse-power  are  necessary  for  the 
present  transmission.  At  $7.50  per  horse-power  capacity,  the  first  cost 
of  these  transformers  is  $i  50,000. 

Before  the  weight  and  cost  of  line  conductors  can  be  determined,  the 
voltage  at  which  the  transmission  shall  be  carried  out  and  the  percentage 
of  the  energy  to  be  lost  in  the  conductors  at  periods  of  maximum  load 
must  be  decided  on.  The  voltage  to  be  used  is  a  matter  of  engineering 
judgment,  based  in  large  part  on  experience,  and  cannot  be  determined 
by  calculation.  In  a  transmission  of  100  miles  the  cost  of  conductors  is 
certain  to  be  a  very  heavy  item,  and,  as  this  cost  decreases  as  the  square 
of  the  voltage  goes  up,  it  is  desirable  to  push  the  voltage  as  high  as  the 
requirements  for  reliable  service  permit. 

A  transmission  line  142  miles  long,  from  the  mountains  to  Oakland, 
Cal.,  has  been  in  constant  and  successful  use  for  several  years  with 
40,000  volts  pressure.  This  line  passes  through  wet  as  well  as  dry  cli- 
mate. It  seems  safer  to  conclude,  therefore,  that  40,000  volts  may  be 
used  in  most  places  with  good  results. 

Having  decided  on  the  amount  of  power  and  the  voltage  and  length  of 
the  transmission,  the  required  weight  of  conductors  will  vary  inversely 
as  the  percentage  of  energy  lost  as  heat  in  the  line.  The  best  percentage 


22      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

of  loss  depends  on  the  number  of  factors,  some  of  which,  such  as  the  cost 
of  energy  at  the  generating  plant,  are  peculiar  to  each  case. 

As  a  provisional  figure,  based  in  part  on  the  practice  elsewhere,  the 
loss  on  the  line  here  considered  may  be  taken  at  10  per  cent,  when  trans- 
mitting the  full  load  of  10,000  horse-power.  If  the  line  is  constructed 
on  this  basis  the  percentage  of  loss  will  be  proportionately  less  for  -any 
smaller  load.  Thus,  when  the  line  is  transmitting  only  5,000  horse- 
power, the  loss  will  amount  to  5  per  cent.  During  the  greater  portion 
of  each  day  the  demand  for  power  is  certain  to  be  less  than  the  maximum 
figure,  so  that  a  maximum  loss  of  10  per  cent  will  correspond  to  an  aver- 
age loss  on  all  the  power  delivered  to  the  line  of  probably  less  than  7 
per  cent. 

In  order  to  deliver  10,000  horse-power  by  the  transformers  at  a  re- 
ceiving station  from  a  generating  plant  100  miles  distant  where  the  press- 
ure is  40,000  volts,  the  copper  conductors  must  have  a  weight  of  about 
1,500,000  pounds,  if  the  loss  of  energy  in  them  is  10  per  cent  of  the  energy 
delivered  to  the  line.  Taking  these  conductors  at  a  medium  price  of  15 
cents  per  pound,  their  cost  amounts  to  $225,000. 

The  combined  cost  of  the  transformers,  pole  line,  and  line  conductors, 
as  now  estimated,  amounts  to  $445,000.  No  account  is  taken  of  the 
right-of-way  for  the  pole  line,  because  in  many  cases  this  would  cost 
nothing,  the  public  roads  being  used  for  the  purpose ;  in  other  cases  the 
cost  might  vary  greatly  with  local  conditions. 

The  efficiency  of  the  transmission  is  measured  by  the  ratio  of  the 
energy  delivered  by  the  transformers  at  the  receiving  station  for  local  dis- 
tribution to  the  energy  delivered  by  the  generating  plant  to  the  transform- 
ers that  supply  energy  to  the  line  for  transmission.  If  worked  at  full 
capacity  the  large  transformers  here  considered  would  have  an  efficiency 
of  nearly  98  per  cent;  but  as  they  must  work,  to  some  extent,  on  partial 
loads,  the  actual  efficiency  will  hardly  exceed  96  per  cent. 

The  efficiency  of  the  line  conductors  rises  on  partial  loads,  and  may 
be  safely  taken  at  93  per  cent  for  all  of  the  energy  transmitted,  though 
it  is  only  90  per  cent  on  the  maximum  load.  The  combined  efficiencies 
of  the  two  sets  of  transformers  and  the  line  give  the  efficiency  of  the  trans- 
mission, which  equals  the  product  of  0.96  X  0.93  X  0.96,  or  almost 
exactly  85.7  per  cent.  In  other  words,  the  transformers  at  the  water- 
power  station  absorb  1.17  times  as  much  energy  as  the  transformers  at 
the  receiving  station  deliver  to  distribution  lines  in  the  place  of  use. 

Interest,  maintenance,  and  depreciation  of  this  complete  transmis- 
sion system  are  sufficiently  provided  for  by  an  allowance  of  1 5  per  cent 


COSr  OF  CONDUCTORS  FOR  TRANSMISSION.        23 

yearly  on  its  entire  first  cost.  As  the  total  first  cost  of  the  transmission 
system  was  found  to  be  $445,000,  the  annual  expense  of  interest,  de- 
preciation, and  repairs  at  15  per  cent  of  this  sum  amounts  to  $66,750. 

In  order  to  find  the  bearings  of  this  annual  charge  on  the  cost  of 
power  transmission  the  total  amount  of  energy  transmitted  annually  must 
be  determined.  The  10,000  horse-power  delivered  by  the  system  at  the 
sub-station  is  simply  the  maximum  rate  at  which  energy  may  be  supplied, 
and  the  element  of  time  must  be  introduced  in  order  to  compute  the 
amount  of  transmitted  energy.  If  the  system  could  be  kept  at  work  dur- 
ing twenty-four  hours  a  day  at  full  capacity,  the  delivered  energy  would 
be  represented  by  the  product  of  the  numbers  which  stand  for  the  capac- 
ity and  for  the  total  number  of  hours  yearly. 

Unfortunately,  however,  the  demands  for  electric  light  and  power 
vary  through  a  wide  range  in  the  course  of  each  twenty-four  hours,  and 
the  period  of  maximum  demand  extends  over  only  a  small  part  of  each 
day.  The  problem  is,  therefore,  to  find  what  relation  the  average  load 
that  may  be  had  during  the  twenty-four  hours  bears  to  the  capacity  re- 
quired to  carry  this  maximum  load.  As  the  answer  to  this  question  de- 
pends on  the  power  requirements  of  various  classes  of  consumers,  it  can 
be  obtained  only  by  experience.  It  has  been  found  that  some  electric 
stations,  working  twenty-four  hours  daily  on  mixed  loads  of  lamps  and 
stationary  motors,  can  deliver  energy  to  an  amount  represented  by  the 
necessary  maximum  capacity  during  about  3,000  hours  per  year.  Ap- 
plying this  rule  to  the  present  case,  the  transformers  at  the  sub-station, 
if  loaded  to  their  maximum  capacity  of  10,000  horse-power  by  the  heavi- 
est demands  of  consumers,  may  be  expected  to  deliver  energy  to  the 
amount  of  3,000  X  10,000  =  30,000,000  horse-power  hours  yearly. 

The  total  cost  of  operation  for  this  transmission  system  was  found 
above  to  be  $66,750  per  annum,  exclusive  of  the  cost  of  energy  at  the  gen- 
erating plant.  This  sum,  divided  by  30,000,000,  shows  the  cost  of  energy 
transmission  to  be  0.222  cent  per  horse-power  hour,  exclusive  of  the  first 
cost  of  the  energy.  To  obtain  the  total  cost  of  transmission,  the  figures 
just  given  must  be  increased  by  the  value  of  the  energy  lost  in  trans- 
formers and  in  the  line  conductors.  In  order  to  find  this  value,  the  cost 
of  energy  at  the  generating  plant  must  be  known. 

The  cost  of  electrical  energy  at  the  switchboard  in  a  water-power  sta- 
tion is  subject  to  wide  variations,  owing  to  the  different  investments 
necessary  in  the  hydraulic  work  per  unit  of  power  developed.  With 
large  powers,  such  as  are  here  considered,  a  horse-power  hour  of  elec- 
trical energy  may  be  developed  for  materially  less  than  0.5  cent  in  some 


24      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

plants.  A's  the  average  efficiency  of  the  present  transmission  has  been 
found  to  be  85.7  per  cent  of  the  energy  delivered  by  the  generators,  it  is 
evident  that  1.17  horse-power  hours  must  be  drawn  from  the  generators 
for  every  horse-power  hour  supplied  by  the  transformers  at  the  sub- 
station for  distribution.  In  other  words,  o.  1 7  horse-power  hour  is  wasted 
for  each  horse-power  hour  delivered. 

The  cost  of  0.17  of  a  horse-power  hour,  or  say  not  more  than  0.5  X 
0.17  =0.085  cent,  must  thus  be  added  to  the  figures  for  transmission 
cost  already  found,  that  is,  0.222  cent  per  horse-power  hour,  to  obtain 
the  total  cost  of  transmission.  The  sum  of  these  two  items  of  cost 
amounts  to  0.307  cent  per  horse-power  hour,  as  the  entire  transmission 
expense. 

It  may  now  be  asked  how  the  cost  of  transmission  just  found  will  in- 
crease if  the  distance  be  extended.  As  an  illustration,  assume  the  length 
of  the  transmission  to  be  150  instead  of  100  miles.  Let  the  amount  of 
energy  delivered  by  the  sub-station,  the  loss  in  line  conductors,  and  the 
energy  drawn  from  the  generating  plant  remain  the  same  as  before. 
Evidently  the  cost  of  the  pole  line  will  be  increased  50  per  cent,  that  is, 
from  $70,000  to  $105,000.  Transformers,  having  the  same  capacity,  will 
not  be  changed  from  the  previous  estimate  of  #i  50,000.  If  the  voltage 
of  the  transmission  remain  constant,  as  well  as  the  line  loss  at  maximum 
load,  the  weight  and  cost  of  copper  conductors  must  increase  with  the 
square  of  the  distances  of  transmission.  For  150  miles  the  weight  of 
copper  will  thus  be  2.25  times  the  weight  required  for  the  loo-mile 
transmission. 

Instead  of  an  increase  in  the  weight  of  conductors  a  higher  voltage 
may  be  adopted.  The  transformers  for  the  two  great  transmission 
systems  that  extend  over  a  distance  of  about  1 50  miles,  from  the  Sierra 
Nevada  Mountains  to  San  Francisco  Bay,  in  California,  are  designed 
to  deliver  energy  to  the  line  at  either  40,000  or  60,000  volts,  as  desired. 
Though  the  regular  operation  at  first  was  at  the  lower  pressure,  the 
voltage  has  been  raised  to  60,000. 

The  lower  valleys  of  the  Sacramento  and  the  San  Joaquin  rivers, 
which  are  crossed  by  these  California  systems,  as  well  as  the  shores  of 
San  Francisco  Bay,  have  as  much  annual  precipitation  and  as  moist  an 
atmosphere  as  most  parts  of  the  United  States  and  Canada.  There- 
fore there  seems  to  be  no  good  reason  to  prevent  the  use  of  60,000  volts 
elsewhere. 

The  distance  over  which  energy  may  be  transmitted  at  a  given  rate, 
with  a  fixed  percentage  of  loss  and  a  constant  weight  of  copper,  goes  up 


COST  OF  CONDUCTORS  FOR  TRANSMISSION.        25 

directly  with  the  voltage  employed.  This  rule  follows  because,  while  the 
weight  of  conductors  to  transmit  energy  at  a  given  rate,  with  a  certain 
percentage  of  loss  and  constant  voltage,  increases  as  the  square  of  the 
distance,  the  weight  of  conductors  decreases  as  the  square  of  the  voltage 
when  all  the  other  factors  are  constant. 

Applying  these  principles  to  the  i5o-mile  transmission,  it  is  evi- 
dent that  an  increase  of  the  voltage  to  60,000  will  allow  the  weight 
of  conductors  to  remain  exactly  where  it  was  for  the  transmission  of 
100  miles,  the  rate  of  working  and  the  line  loss  being  equal  for  the  two 
cases. 

The  only  additional  item  of  expense  in  the  1 5o-mile  transmission,  on 
the  basis  of  60,000  volts,  is  the  $35,000  for  pole  line.  Allowing  15  per 
cent  on  the  $35,000  to  cover  interest,  depreciation,  and  maintenance,  as 
before,  makes  a  total  yearly  increase  in  the  costs  of  transmission  of  $5,250 
over  that  found  for  the  transmission  of  i  oo  miles.  This  last  sum  amounts 
to  0.0175  cent  per  horse-power  hour  of  the  delivered  energy. 

The  cost  of  transmission  is  thus  raised  to  0.307  -|-  0.0175  —  0.324 
cent  per  horse-power  hour  of  delivered  energy  on  the  i5o-mile  system 
with  60,000  volts. 

Existing  transmission  lines  not  only  illustrate  the  relations  of  the 
factors  named  above  to  the  cost  and  weight  of  conductors,  but  also  show 
marked  variations  of  practice,  corresponding  to  the  opinions  of  different 
engineers.  In  order  to  bring  out  the  facts  on  these  points,  the  data  of  a 
number  of  transmission  lines  are  here  presented.  On  these  lines  the  dis- 
tance of  transmission  varies  between  5  and  142  miles,  the  voltage  from 
5,000  to  50,000,  and  the  maximum  rate  of  work  from  a  few  hundred  to 
some  thousands  of  horse-power.  For  each  transmission  the  single  length 
and  total  weight  of  conductors,  the  voltage,  and  the  capacity  of  the  gen- 
erating equipment  that  supplies  the  line  is  recorded.  From  these  data 
the  volts  per  mile  of  line,  weight  and  cost  of  conductors  per  kilowatt  ca- 
pacity of  generating  equipment,  and  the  weight  of  conductors  per  mile 
for  each  kilowatt  of  capacity  in  the  generating  equipment  are  calcu- 
lated. In  each  case  the  length  of  line  given  is  the  distance  from  the  gen- 
erating to  the  receiving  station.  The  capacity  given  for  generating  equip- 
ment in  each  case  is  that  of  the  main  dynamos,  where  their  entire  output 
goes  to  the  transmission  line  in  question,  but  where  the  dynamos  supply 
energy  for  other  purposes  also,  the  rating  of  the  transformers  that  feed 
only  the  particular  transmission  line  is  given  as  the  capacity  of  generat- 
ing equipment. 

The  transmission  systems  here  considered  have  been  selected  because 


26      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

it  was  possible  to  obtain  the  desired  data  as  to  each,  and  it  may  be  pre- 
sumed that  they  fairly  illustrate  present  practice.  It  may  be  noted  at 
once  that  in  general  the  line  voltage  is  increased  with  the  length  of  the 
transmission.  Thus,  the  transmission  for  the  Ludlow  Mills  over  a  dis- 


DlSTANCE  AND  VOLTAGE  OF  ELECTRICAL  TRANSMISSION. 


Distance  in 
Miles. 

Volts. 

Volts  per 
Mile. 

Colgate  to  Oakland,  Cal  

14.2 

60,000 

422 

Canon  Ferry  to  Butte,  Mont  

6<; 

50,000 

760 

Santa  Ana  River  to  Los  Angeles  
Ogden  to  Salt  Lake  City  Utah 

83 
•26    C 

33,000 
1  6  ooo 

397 
4.38 

Madrid  to  Bland,  N.  M. 

6^-J 

•22 

20,000 

46° 
62$ 

Welland  Canal  to  Hamilton,  Can..  . 

San  Gabriel  Canon  to  Los  Angeles.  . 
Canon  City  to  Cripple  Creek,  Colo.  . 
Apple  River  to  St.  Paul,  Minn  

]3» 

(37 

23    , 
23-5 

2C 

22,500 
16,000 

20,000 
25,OOO 

643 

695 
851 
I,  OOO 

Yadkin  River  to  Salem  N  C 

14.    ^ 

12  OOO 

827 

Into  Victor  Colo 

8 

12  6OO 

I  ^7^ 

M^ontmorency  Falls  to  Quebec 

7' 

5   TOO 

78< 

Farmington  River  to  Hartford  
SewalFs  Falls  to  R.R.  shops  Concord 
"\Vilbraham  to  Ludlow  Mills 

ii 

5-5 

4e 

10,000 
10,000 

1  1  500 

909 

1,818 

2  t  e  £ 

To  Dales  Ore 

27 

22  OOO 

Sid. 

tance  of  4.5  miles  is  carried  out  at  11,500  volts.  On  the  other  hand,  the 
transmission  between  Canon  Ferry  and  Butte,  a  distance  of  65  miles,  em- 
ploys 50,000  volts  and  represents  recent  practice.  The  system  from 
Colgate  to  Oakland,  a  distance  of  142  miles,  the  longest  here  considered, 
now  has  60,000  volts  on  its  lines.  In  spite  of  the  general  resort  to  high 
pressures  with  greater  distances  of  transmission,  the  rise  in  voltage  has 
not  kept  pace  with  the  increasing  length  of  line.  For  the  Wilbraham- 
Ludlow  transmission  the  total  pressure  amounts  to  2,555  vo^ts  Per  mile> 
while  the  line  from  Colgate  to  Oakland  with  31.5  times  the  length  of  the 
former  operates  at  an  average  of  only  422  volts  per  mile.  Of  the  fifteen 
transmissions  considered,  six  are  over  distances  of  less  than  15  miles, 
and  for  four  of  the  six  the  voltage  is  more  than  900  per  mile.  Eight 
transmissions  range  from  23  to  83  miles  in  length,  with  voltages  that 
average  between  1,000  volts  per  mile  at  25  miles  and  only  397  per  mile 
on  the  83 -mile  line.  The  volts  per  mile  are  6  times  as  great  in  the 
Ludlow  as  in  the  Oakland  transmission. 

These  wide  variations  in  the  volts  per  mile  on  transmission  lines  and 


COST  OF  CONDUCTORS  FOR  TRANSMISSION.        27 


in  length  of  lines  lead  to  different  weights  of  conductors  per  kilowatt 
of  generator  capacity.  All  other  factors  remaining  constant,  the  weight 
of  conductors  per  kilowatt  of  generator  capacity  would  be  the  same  what- 

CAPACITY  OF  GENERATING  STATIONS  AND  WEIGHT  OF  CONDUCTORS. 


Location  of  Transmission. 

Kilowatt 
Capacity  at 
Generators. 

Total  Weight 
of 
Conductors. 

Pounds  of 
Conductors 
per  Kilowatt 
Capacity. 

Wilbraham  to  Ludlow  

4,600 

17  820 

,   7* 

Se  wall's  Falls  to  railroad  shops  

4?o 

6,0  1  4 

I  r 

Into  Victor  Colo.  .  .  . 

600 

i  ^  060 

To  Dales,  Ore. 

ooo 

•7-2  Q7Q 

Apple  River  to  St.  Paul 

,000 

I  <o  600 

O^ 
e  7 

Farmington  River  to  Hartford  

,^oo 

C.4  OC.4 

II 

Canon  City  to  Cripple  Creek  

,<oo 

CQ  O7O 

•7Q 

Yadkin  River  to  Salem 

COO 

rR  O73. 

IVlontmorency  Falls  to  Quebec 

2  4OO 

1  80  O?6 

OV 
*7O 

Canon  Ferry  to  Butte 

57OO 

6^8  ^°o 

/y 
1  1  C 

San  Gabriel,  Canon  to  Los  Angeles.. 
\Velland  Canal  to  Hamilton  . 

1,200 
6,OOO 

73,002 

•276  4O4 

i5 

61 
61 

Madrid  to  Bland,  N.  M. 

600 

127  680 

212 

Ogden  to  Salt  Lake  City    

2,2<O 

2O2   ^6c. 

I2Q 

Santa  Ana  River  to  Los  Angeles  
Colgate  to  Oakland 

2,250 

I  I      2^O 

664,830 
j  906,954 

295 

81 

]  446,627 

40* 

*  Aluminum. 

ever  the  length  of  the  transmission,  provided  that  the  volts  per  mile  were 
uniform  for  all  cases.  One  important  factor,  the  percentage  of  loss  for 
which  the  line  conductors  are  designed  at  full  load,  is  sure  to  vary  in  dif- 
ferent cases,  and  lead  to  corresponding  variations  in  the  weights  of  con- 
ductors per  kilowatt  of  generator  capacity.  In  conductors  of  equal 
length  one  pound  of  aluminum  has  nearly  the  same  electrical  resistance 
as  two  pounds  of  copper,  and  this  ratio  must  be  allowed  for  when  cop- 
per and  aluminum  lines  are  compared. 

From  the  table  it  may  be  seen  that  the  weight  of  conductors  per  kilo- 
watt of  generator  capacity  for  the  transmission  from  Santa  Ana  River  is 
29.5  times  as  great  as  the  like  weight  for  the  line  into  Victor.  But  the 
volts  per  mile  are  four  times  as  great  on  the  Victor  as  they  are  on  the 
Santa  Ana  River  line.  The  extreme  range  of  the  cases  presented  is  that 
between  the  Ludlow  plant,  with  the  equivalent  of  7.4  pounds,  and  the 
Santa  Ana  River  system  with  295  pounds  of  copper  conductors  per  kilo- 
watt of  generator  capacity.  Three  transmissions  with  1,575  to  2>555 


28      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


volts  per  mile  have  the  equivalent  of  7.4  to  15  pounds  of  copper  each,  pet 
kilowatt  of  generator  capacity. 

Of  the  seven  transmissions  using  between  36  and  79  pounds  of  cop^ 
per  for  each  kilowatt  of  generator  capacity,  four  have  voltages  ranging 
from  827  to  1,000  per  mile,  and  on  only  one  is  the  pressure  as  low  as 
643  volts  per  mile.  Five  transmission  lines  vary  between  115  and  295 
pounds  of  copper,  or  its  equivalent,  per  kilowatt  of  generator  capacity, 
and  their  voltages  per  mile  are  as  high  as  769  in  one  case  and  down  to 
281  in  another.  Allowing  for  some  variations  in  the  percentages  of  loss 
in  transmission  lines  at  full  load,  the  fifteen  plants  plainly  illustrate  the  ad-  . 
vantage  of  a  high  voltage  per  mile,  as  to  the  weight  of  conductors.  This 
advantage  is  especially  clear  if  the  differences  due  to  the  lengths  of  the 
transmissions  are  eliminated  by  dividing  the  weight  of  conductors  per 
kilowatt  of  generator  capacity  in  each  case  by  the  length  of  the  transmis- 
sion in  miles.  This  division  gives  the  weight  of  conductors  per  kilowatt 
of  generators  for  each  mile  of  the  line,  which  may  be  called  the  weight 


WEIGHT  AND  COST  OF  CONDUCTORS. 


Pounds  per 
Kilowatt 

Mile. 

Dollars  per 
Generator 
Kilowatt. 

o  86* 

ill 

Se  wall's  Falls  to  railroad  shops  

2  7 

2  2< 

Into  Victor,  Colo  

O  0 

I   ^O 

To  Dales,  Ore. 

5IO 

Apple  River  to  St.  Paul 

2  I 

•AV-* 
7  O< 

Farmington  River  to  Hartford 

32 

/•vo 
10  80 

Canon  Citv  to  Cripple  Creek  .  . 

i  6 

z  8< 

Yadkin  River  to  Salem  

2  6 

*  8s 

Montmorency  Falls  to  Quebec  ..... 

112 

j-'-'j 
ii.Sq 

Canon  Ferry  to  Butte  

1.7 

17.  2S 

San  Gabriel  Canon  to  Los  Angeles 

2  6 

o  8s 

Welland  Canal  to  Hamilton  . 

I  7 

0  4S 

Madrid  to  BlaoJ,  N.  M. 

66 

31  80 

Ogden  to  Salt  Lake  City  

3e 

10  "?S 

Santa  Ana  Riverto  Los  Angeles  ... 

3.C 

44.  2S 

Colgate  to  Oakland  .  .  

\    -S6 

24.  i«; 

1    .27* 

*Aluminum. 


per  kilowatt  mile.  For  the  Ludlow  transmission  this  weight  is  only  0.86 
pound  of  aluminum,  the  equivalent  of  1.72  pounds  of  copper,  while  the 
like  weight  for  the  line  into  Quebec  is  11.2  pounds  of  copper,  or  6.5  times 


COST  OF  CONDUCTORS  FOR  TRANSMISSION.        29 

that  for  the  former  line.  But  the  voltage  per  mile  on  the  Ludlow  is  3.2 
times  as  great  as  the  like  voltage  on  the  Quebec  line. 

The  weight  of  conductor  per  kilowatt  mile  in  the  Victor  line  is  only 
0.9  pound,  and  the  like  weight  for  the  line  between  Madrid  and  Bland  is 
6.6  pounds,  or  7.3  times  as  great.  On  the  Victor  line  the  voltage  per 
mile  is  2.5  times  as  great  as  the  voltage  for  each  mile  of  the  Bland  line. 

Comparing  systems  with  nearly  equal  voltages  per  mile,  it  appears 
in  most  cases  that  only  such  difference  exists  in  their  pounds  of  conduc- 
tors per  kilowatt  mile  as  may  readily  be  accounted  for  by  designs  for  vari- 
ous percentages  of  loss  at  full  load.  Though  the  transmission  line  into 
Butte  is  nearly  twice  as  long  as  the  one  entering  Hamilton,  the  weight  of 
conductors  for  each  is  i  .7  pounds  per  kilowatt  mile.  The  line  from  Santa 
Ana  River  is  more  than  twice  as  long  as  the  one  entering  Salt  Lake  City, 
but  its  voltage  per  mile  is  only  nine  per  cent  less,  and  there  are  3.5 
pounds  of  copper  in  each  line  per  kilowatt  mile. 

The  final,  practical  questions  as  to  conductors  in  electrical  transmis- 
sion relate  to  their  cost  per  kilowatt  of  maximum  working  capacity,  and 
per  kilowatt  hour  of  delivered  energy.  If  the  cost  of  conductors  per  kilo- 
watt of  generator  capacity  is  greater  than  that  of  all  the  remaining  equip- 
ment, it  is  doubtful  whether  the  transmission  will  pay.  If  fixed  charges 
on  the  conductors  more  than  offset  the  difference  in  the  cost  of  energy  per 
kilowatt  hour  at  the  points  of  development  and  delivery,  it  is  certain  that 
the  generating  plant  should  be  located  where  the  power  is  wanted.  The 
great  cost  of  conductors  is  often  put  forward  as  a  most  serious  impediment 
to  long-distance  transmission,  and  the  examples  here  cited  will  indicate  the 
weight  of  this  argument.  In  order  to  find  the  approximate  cost  of  con- 
ductors per  kilowatt  of  generator  capacity  for  each  of  the  transmission 
lines  here  considered,  the  price  of  bare  copper  wire  is  taken  at  1 5  centsl 
and  the  price  of  bare  aluminum  wire  at  30  cents  per  pound .  In  each  case 
the  weight  of  copper  or  aluminum  conductor  per  kilowatt  of  generator 
capacity  is  used  to  determine  their  costs  per  kilowatt  of  this  capacity  at  the 
prices  just  named.  This  process  when  carried  out  for  the  15  transmis- 
sion lines  shows  that  their  cost  of  conductors  per  kilowatt  of  generator 
capacity  varies  between  #i  .1 1  for  the  4.5  mile  line  into  Ludlow  and  #44.25 
for  the  line  of  83  miles  from  the  Santa  Ana  River.  It  should  be  noted  that 
the  former  of  these  lines  operates  at  2,555  an<^  the  latter  at  397  volts  per 
mile.  The  line  into  Madrid  shows  an  investment  in  conductors  of  #3 1 .80 
per  kilowatt  of  generator  capacity  with  625  volts  per  mile.  That  a  long 
transmission  does  not  necessarily  require  a  large  investment  in  conduc- 
tors per  kilowatt  of  generator  capacity  is  shown  by  the  line  65  miles  long 


30      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

into  Butte,  for  which  the  cost  is  $17.25  per  kilowatt,  with  769  volts  per 
mile.  For  the  transmission  to  St.  Paul,  a  distance  of  25  miles,  at  1,000 
volts  per  mile,  the  cost  of  conductors  is  $7.95  per  kilowatt  of  generator 
capacity.  The  seven-mile  line  into  Quebec  shows  an  investment  of 
$i  i  .85  per  kilowatt  of  generator  capacity. 


CHAPTER  IV. 

ADVANTAGES  OF  THE  CONTINUOUS  AND  ALTERNATING  CURRENT. 

ELECTRICAL  transmission  over  long  distances  in  America  have  been 
mainly  carried  out  with  alternating  current.  In  Europe,  on  the  other 
hand,  continuous  current  is  widely  used  on  long  transmissions  at  high 
voltages.  So  radical  a  difference  in  practice  seems  to  indicate  that 
neither  system  is  lacking  in  points  of  superiority. 

A  fundamental  feature  of  long  transmissions  is  the  high  voltage  neces- 
sary for  economy  in  conductors,  and  this  voltage  is  attained  by  entirely 
different  methods  with  continuous  and  alternating  currents.  In  dyna- 
mos of  several  hundred  or  more  kilowatts  capacity  the  pressure  of  con- 
tinuous current  has  not  thus  far  been  pushed  above  4,000  volts,  because 
of  the  danger  of  sparking  and  flashing  at  the  commutator.  Where  10,000 
or  more  volts  are  required  on  a  transmission  line  with  continuous  current 
a  number  of  dynamos  are  connected  in  series  so  that  the  voltage  of  each 
is  added  to  that  of  the  others.  In  this  way  the  voltage  of  each  dynamo 
may  be  as  low  as  is  thought  desirable  without  limiting  the  total  line  volt- 
age. There  is  no  apparent  limit  to  the  number  of  continuous-current 
dynamos  that  may  be  operated  in  series  or  to  the  voltage  that  may  be 
thus  obtained.  In  the  recently  completed  transmission  from  St.  Maurice 
to  Lausanne,  Switzerland,  with  continuous  current,  ten  dynamos  are  con- 
nected in  series  to  secure  the  line  voltage  of  23,000.  When  occasion  re- 
quires twenty  or  thirty  or  more  dynamos  to  be  operated  in  series,  giving 
50,00001'  75,000  volts  on  the  line,  machines  exactly  like  those  in  the  trans- 
mission just  named,  may  be  used.  No  matter  how  many  of  these  dyna- 
mos are  operated  in  series  the  electric  strain  on  the  insulation  of  the 
windings  of  each  dynamo  remains  practically  constant,  because  the  iron 
frame  of  each  dynamo  is  insulated  in  a  most  substantial  manner  from  the 
ground.  The  electric  strain  on  the  insulation  of  the  windings  of  each 
dynamo  in  the  series  is  thus  limited  to  the  voltage  generated  by  that 
dynamo.  There  is  no  practical  limit  to  the  thickness  or  strength  of  the 
insulation  that  may  be  interposed  between  the  frame  of  each  dynamo 
and  the  ground,  and  hence  no  limit  to  line  voltage  as  far  as  dynamo  in- 
sulation is  concerned. 


32      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

It  is  impracticable  to  operate  alternating  dynamos  in  series  so  as  to 
add  their  voltages,  and  the  pressure  available  in  transmission  with  alter- 
nating current  must  be  that  of  a  single  dynamo  or  must  be  obtained  by 
the  use  of  transformers.  The  voltage  of  an  alternating  may  be  carried 
much  higher  than  that  of  a  continuous-current  dynamo  of  very  large 
capacity,  and  in  many  cases  pressures  of  13,200  volts  are  now  sup- 
plied to  transmission  lines  by  alternating  dynamos.  Just  how  high  the 
voltage  of  single  alternating  dynamos  will  be  carried  no  one  can  say, 
but  it  seems  probable  that  the  practical  limit  will  prove  to  be  much  less 
than  the  voltages  now  employed  in  some  transmissions.  As  the  voltage 
of  alternating  dynamos  is  carried  higher  the  thickness  of  insulation  on 
their  armature  coils  and  consequently  the  size  or  number  of  slots  in 
their  armature  cores  and  the  size  of  these  cores  increase  rapidly.  The 
dimensions  and  weight  of  an  alternating  dynamo  per  unit  of  its  capacity 
thus  go  up  with  the  voltage,  and  at  some  undetermined  point  the  cost 
of  the  high-voltage  dynamo  is  greater  than  that  of  a  low- voltage  dynamo 
of  equal  capacity  with  raising  transformers.  To  the  voltage  that  may 
be  supplied  by  transformers  there  is  no  practical  limit  now  in  sight. 
Lines  have  been  in  regular  operation  from  one  to  several  years  on  which 
transformers  supply 40,000  to  50,000  volts;  some  large  transformers  have 
been  built  for  commercial  use  at  60,000  volts,  and  other  transformers  for 
experimental  and  testing  purposes  have  been  employed  in  a  number  of 
cases  for  pressures  of  100,000  volts  and  more. 

Available  voltages  for  continuous-  and  alternating-current  transmis- 
sions are  thus  on  a  practically  equal  footing  as  to  their  upper  limit.  The 
amount  of  power  that  may  be  generated  and  delivered  with  either  the 
alternating-  or  continuous-current  system  of  transmission  is  practically 
unlimited.  Single  alternating  dynamos  may  be  had  of  5,000  or  even 
8,000  kilowatts  capacity  if  desired,  but  it  is  seldom  that  these  very  large 
units  are  employed,  because  the  capacity  of  a  generating  station  should 
be  divided  up  among  a  number  of  machines.  It  is  perhaps  impractica- 
ble to  build  single  continuous-current  dynamos  with  capacities  equal  to 
those  of  the  largest  alternators,  but  as  any  number  of  the  continuous- 
current  machines  may  be  operated  either  in  series  or  multiple,  the  power 
that  may  be  applied  to  a  transmission  circuit  is  unlimited. 

At  the  plant  or  plants  where  the  power  transmitted  by  continuous 
current  is  received,  a  number  of  motors  must  be  connected  in  series  to 
operate  at  the  high-line  voltage.  These  motors  may  all  be  located  in  a 
single  room,  may  be  connected  to  machinery  in  different  parts  of  a  build- 
ing, or  may  be  in  use  at  points  miles  apart.  The  vital  requirement  is  that 


CONTINUOUS  AND  ALTERNATING  CURRENT.       33 

the  motors  must  be  in  series  with  each  other  so  that  the  line  voltage 
divides  between  them.  If  simply  mechanical  power  is  wanted  at  the 
places  where  the  motors  are  located,  they  complete  the  transmission 
system  and  no  further  electrical  apparatus  is  required.  Where,  however, 
as  at  Lausanne,  the  transmitted  power  is  to  be  used  in  a  system  of  gen- 
eral electrical  supply,  the  motors  that  receive  the  current  at  the  line  volt- 
age must  drive  dynamos  that  will  deliver  energy  of  the  required  sorts. 
In  the  station  at  Lausanne  four  of  the  motors  to  which  the  transmission 
line  is  connected  each  drives  a  3,000- volt  three-phase  alternator  for  the 
distribution  of  light  and  power.  The  fifth  motor  at  this  station  drives  a 
6oo-volt  dynamo  which  delivers  continuous  current  to  a  street  railway. 
A  sixth  motor  in  the  same  series  drives  a  cement  factory  some  distance 
from  the  station.  Neglecting  minor  changes  in  capacity  due  to  losses 
in  the  line  and  motors,  this  continuous-current  system  must  thus  include 
three  kilowatts  in  motors  and  dynamos  for  each  kilowatt  delivered  for 
general  electrical  distribution  at  the  receiving  station.  In  a  case  in  which 
only  mechanical  power  is  wanted  at  the  receiving  station,  the  dynamos 
and  motors  concerned  in  the  transmission  must  have  a  combined  capac- 
ity of  two  horse-power  for  each  horse-power  delivered  at  the  motor 
shaft.  In  contrast  with  these  figures,  the  electrical  equipment  in  a  trans- 
mission with  alternating  current  for  mechanical  power  alone  includes  two 
kilowatts  capacity  in  generators  and  motors,  besides  two  kilowatts  ca- 
pacity in  transformers  for  each  corresponding  unit  of  power  delivered 
at  the  motor  shaft  unless  generators  and  motors  operate  at  the  full 
line  voltage.  If  a  general  electrical  supply  is  to  be  operated  by  the  alter- 
nating system  of  transmission,  either  motors  and  dynamos  or  rotary 
converters  must  be  added  to  transformers  where  continuous  current  is 
required.  An  alternating  transmission  may  thus  include  as  little  as 
one  kilowatt  in  dynamos  and  one  in  transformers,  or  as  much  as  two 
kilowatts  capacity  in  dynamos,  two  in  transformers,  and  one  in  mo- 
tors for  each  kilowatt  delivered  to  distribution  lines  at  the  receiving 
station. 

Line  construction  from  the  continuous-current  transmission  is  of  the 
most  simple  character  apart  from  the  necessity  of  high  insulation.  Only 
two  wires  are  necessary  and  they  may  be  of  any  desired  cross-section, 
strung  on  a  single  pole  line  and  need  not  be  transposed.  On  these  wires 
the  maximum  voltage  for  which  insulation  must  be  provided  is  the  nom- 
inal voltage  of  the  system.  It  is  possible  under  these  conditions  to  build 
a  single  transmission  line  with  two  conductors  of  such  size  and  strength 
and  at  such  a  distance  apart  that  a  high  degree  of  reliability  is  attained 
3 


34      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

against  breaks  in  the  wires  or  arcing  between  them.  In  a  transmis- 
sion of  power  by  two-  or  three-phase  alternating  current  at  least  three 
wires  are  necessary  and  six  or  more  are  often  employed.  If  six  or 
more  wires  carrying  current  at  the  high  voltages  required  by  long  trans- 
missions are  mounted  on  a  single  line  of  poles,  it  is  not  practicable  to 
obtain  such  distances  between  the  wires  as  are  desirable.  The  repair  of 
one  set  of  wires  while  the  other  set  is  in  operation  is  a  dangerous  task, 
and  an  arc  originating  between  one  set  of  the  wires  is  apt  to  be  com- 
municated to  another  set.  For  these  reasons  two  pole  lines  are  frequently 
provided  for  a  transmission  with  alternating  current,  and  three  or  more 
wires  are  then  erected  on  each  line.  Compared  with  a  continuous-cur- 
rent transmission,  one  with  alternating  current  often  requires  more  poles 
and  is  quite  certain  to  require  more  cross-arms,  pins,  insulators,  and  labor 
of  erection.  For  a  given  effective  voltage  of  transmission  it  is  harder 
to  insulate  an  alternating-  than  a  continuous-current  line.  In  the  first 
place  the  maximum  voltage  of  the  alternating  line  with  even  a  true  sine 
curve  of  pressure  is  1.4  times  the  nominal  effective  voltage,  but  the 
insulation  must  withstand  the  maximum  pressure.  Then  comes  the 
matter  of  resonance,  which  may  carry  the  maximum  voltage  of  an  alter- 
nating circuit  up  to  several  times  its  normal  amount,  if  the  period  of 
electrical  vibration  for  that  particular  circuit  should  correspond  to  the 
frequency  of  the  dynamos  that  operate  it.  Even  where  the  vibration 
period  of  a  transmission  circuit  and  the  frequency  of  its  dynamos  do  not 
correspond,  and  good  construction  should  always  be  planned  for  this 
lack  of  agreement,  resonance  may  and  often  does  increase  the  normal 
voltage  of  an  alternating  transmission  by  a  large  percentage.  The  alter- 
nating system  of  transmission  must  work  at  practically  constant  voltage 
whatever  the  state  of  its  load,  so  that  the  normal  stress  on  the  insulation 
is  always  at  its  maximum.  In  a  transmission  with  continuous  current 
on  the  other  hand,  if  the  prevailing  practice  of  a  constant  current  and 
varying  pressure  on  the  line  is  followed,  the  insulation  is  subject  to  the 
highest  voltage  only  at  times  of  maximum  load  on  the  system.  Lightning 
is  a  very  real  and  pressing  danger  to  machinery  connected  to  long  trans- 
mission lines,  and  this  danger  is  much  harder  to  guard  against  in  an 
alternating  system  than  in  a  system  with  continuous  constant  current. 
The  large  degree  of  exemption  from  damage  by  lightning  enjoyed  by 
series  arc  dynamos  is  well  known,  the  magnet  windings  of  such  machines 
acting  as  an  inductance  that  tends  to  keep  lightning  out  of  them.  More- 
over, with  any  continuous-current  machines  lightning  arresters  having 
large  self-induction  may  be  connected  in  circuit  and  form  a  most  effective 


CONTINUOUS  AND  ALTERNATING  CURRENT.       35 

safeguard  against  lightning,  but  this  plan  is  not  practicable  on  alternat- 
ing lines. 

In  the  matter  of  switches,  controlling  apparatus,  and  switchboards, 
an  alternating  transmission  requires  much  more  equipment  than  a  sys- 
tem using  continuous,  constant  current.  The  ten  dynamos  in  the  gen- 
erating station  at  St.  Maurice,  with  a  capacity  of  3,450  kilowatts  at  23,000 
volts,  are  each  connected  and  disconnected  with  the  transmission  by  a 
switch  in  a  small  circular  column  of  cast-iron  that  stands  hardly  breast 
high.  An  amperemetre  and  voltmetre  are  mounted  on  each  dynamo. 
The  alternating  generators  in  a  station  of  equal  capacity  and  voltage 
would  require  a  large  switchboard  fitted  with  bus-bars,  oil  switches,  and 
automatic  circuit-breakers.  Relative  efficiencies  for  the  continuous- 
current  and  the  alternating-transmission  systems  vary  with  the  kind  of 
service  required  at  receiving  stations  and  with  the  extent  to  which  trans- 
formers are  used  in  the  alternating  system,  other  factors  being  constant. 
For  purposes  of  comparison  the  efficiency  at  full  load  of  both  alternating- 
and  continuous-current  dynamos  and  motors,  also  of  rotary  converters, 
may  be  fairly  taken  at  92  per  cent,  and  the  efficiency  of  transformers  at 
96  per  cent. 

For  the  line  an  efficiency  of  94  per  cent  may  be  assumed  at  full  load, 
this  being  the  actual  figure  in  one  of  the  Swiss  transmissions  of  2,160 
kilowatts  at  14,400  volts  to  a  distance  of  32  miles.  Where  the  continuous 
current  system  must  simply  deliver  mechanical  power  at  the  receiving 
stations,  its  efficiency  under  full  load  amounts  to92X-94X-92  = 
79.65  per  cent  from  dynamo  shaft  to  motor  shaft.  An  alternating  sys- 
tem delivering  mechanical  power  will  have  an  efficiency  of  92  x  -94  X 
.96  x  -92  =  76.46  per  cent  between  dynamo  shaft  and  motor  shaft,  if 
the  line  voltage  is  generated  in  the  armature  coils  of  the  dynamo  and 
the  line  loss  is  6  per  cent.  If  step-up  transformers  are  employed  to 
secure  the  line  voltage  the  efficiency  of  the  alternating  transmission  de- 
livering mechanical  power  drops  to  the  figure  of  92  x  -96  X  -94  X  -96 
X  .92  =  73.40  per  cent.  It  thus  appears  that  for  the  simple  delivery 
of  mechanical  power  the  continuous  current  transmission  has  an  advan- 
tage over  the  alternating  of  three  to  six  per  cent  in  efficiency,  depending 
on  whether  step-up  transformers  are  employed. 

When  the  receiving  station  must  deliver  a  supply  of  either  continuous 
or  alternating  current  for  general  distribution,  the  efficiency  of  the  con- 
tinuous-current transmission  amounts  to  92  x  -94  X  -92  X  -92  =  73-27 
per  cent.  The  alternating-transmission  system  in  a  case  in  which  no  step- 
up  transformers  are  employed  will  deliver  alternating  current  of  the  same 


36      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

frequency  as  that  on  the  transmission  line  at  any  desired  pressure  for 
general  distribution  at  an  efficiency  of  92  x  -94  X  -96  =  83.02  per  cent, 
if  step-down  transformers  are  used,  brut  the  efficiency  drops  to  83.02  x 
.96  =  79.70  per  cent,  when  step-up  transformers  are  introduced.  If 
the  alternating  transmission  uses  no  step-up  transformers  and  delivers 
either  alternating  or  continuous  current  by  means  of  motor  generators, 
its  efficiency  at  full  load  is  83 .02  x  -92  X  -92  =  70.26  per  cent,  but  with 
step-up  transformers  added  the  efficiency  drops  to  70.26  x  -96  =  67.43 
per  cent.  In  a  transmission  where  electrical  energy  must  be  delivered 
for  general  distribution,  the  full-load  efficiency  of  an  alternating  system 
ranges  either  higher  or  lower  than  that  of  a  continuous-current  system 
depending  on  whether  the  current  from  the  transmission  line  must  be 
converted  or  not. 

Line  loss  is  the  same  whatever  the  load  in  a  constant-current  trans- 
mission, so  that  line  efficiency  falls  rather  rapidly  with  the  load.  On  the 
other  hand,  at  constant  pressure  the  percentage  of  energy  loss  on  the  line 
varies  directly  with  the  load,  but  the  actual  rate  of  energy  loss  with  the 
square  of  the  load.  On  partial  loads  the  line  efficiency  is  thus  much 
higher  with  alternating  than  with  continuous  constant  current. 

Efficiency  of  electrical  machinery  is  generally  low  at  partial  loads,  so 
that  in  cases  in  which  the  number  or  capacity  of  alternating  dynamos, 
transformers,  motors,  or  rotary  converters  for  a  transmission  would  be 
greater  per  unit  of  delivered  power  than  the  corresponding  number  or 
capacity  of  machines  for  a  transmission  by  continuous  current,  the  latter 
would  probably  have  the  advantage  in  the  combined  efficiency  of  ma- 
chinery at  partial  loads.  In  this  way  the  lower-line  efficiency  of  one  sys- 
tem might  offset  the  lower  efficiency  of  machinery  in  the  other.  Energy 
is  usually  very  cheap  at  the  generating  station  of  a  transmission  system. 
For  this  reason  small  differences  in  the  efficiencies  of  different  systems 
should  be  given  only  moderate  weight  in  comparison  with  the  items  of 
first  cost,  reliability,  and  expense  of  operation. 

In  the  matter  of  first  cost  at  least  the  continuous-current  system  seems 
to  have  a  distinct  advantage  over  the  alternating.  Without  going  into  a 
detailed  estimate,  it  is  instructive  to  consider  the  figures  given  by  a  body 
of  five  engineers  selected  to  report  on  the  cost  of  continuous-  and  alternat- 
ing-current equipments  for  the  St.  Maurice  and  Lausanne  transmission. 
According  to  the  report  of  these  engineers,  a  three-phase  transmission  sys- 
tem would  have  cost  $140,000  more  than  the  continuous-current  system 
actually  installed,  all  other  factors  remaining  constant.  It  should  be  noted 
that  the  conditions  of  this  transmission  are  favorable  to  three-phase  work- 


CONTINUOUS  AND  ALTERNATING  CURRENT.       37 

ing  and  unfavorable  to  continuous-current  equipment,  because  all  of  the 
energy  except  that  going  to  the  400  horse-power  motor  at  the  cement  mill 
must  be  delivered  at  the  receiving  station  for  general  distribution.  More- 
over, four  out  of  the  five  motors  at  Lausanne  drive  three-phase  generators, 
and  only  one  drives  a  continuous-current  dynamo  for  the  electric  railway, 
so  that  a  three-phase  transmission  would  have  required  only  one  rotary 
converter.  Had  the  transmission  been  concerned  merely  with  the  de- 
livery of  mechanical  power,  as  at  the  cement  mill,  the  advantage  of  the 
continuous-  over  the  alternating-current  system  in  the  matter  of  first  cost 
would  have  been  much  greater  than  it  was. 

Long-distance  transmission  with  three-phase  current  began  at  Frank- 
fort, in  1891,  when  58  kilowatts  were  received  over  a  2 5,000- volt  line 
from  Lauffen,  109  miles  away.  Shortly  after  this  historic  experiment, 
three-phase  transmission  in  the  United  States  began  on  a  commercial 
scale,  and  plants  of  this  sort  have  multiplied  rapidly  here.  Meantime 
very  little  has  been  done  in  America  with  continuous  currents  in  long 
transmissions.  In  Europe,  the  birthplace  of  the  three-phase  system,  it 
has  failed  to  displace  continuous  current  for  transmission  work.  About 
a  score  of  these  continuous-current  transmissions  are  already  at  work 
there.  If  the  opinion  of  European  engineers  as  to  the  lower  cost  of  the 
continuous-current  system,  all  other  factors  being  equal,  is  confirmed  by 
experience,  this  current  will  yet  find  important  applications  to  long  trans- 
missions in  the  United  States. 

Systems  of  transmission  with  continuous-current  may  operate  at  con- 
stant voltage  and  variable  current,  at  constant  current  and  variable  volt- 
age, or  with  variations  of  both  volts  and  amperes  to  correspond  with 
changes  of  load.  Dynamos  of  several  thousand  kilowatts  capacity  each 
can  readily  be  had  at  voltages  of  500  to  600,  but  the  attempt  to  con- 
struct dynamos  to  deliver  more  than  two  or  three  hundred  kilowatts 
each  at  several  thousand  volts  has  encountered  serious  sparking  at  the 
commutator.  Thus  far,  dynamos  that  yield  between  300  and  400  kilo- 
watts each  have  been  made  to  give  satisfactory  results  at  pressures  as  high 
as  2,500  volts. 

Another  one  of  the  Swiss  transmissions  takes  place  over  a  distance  of 
thirty- two  miles  at  14,400  volts,  the  capacity  being  2,160  kilowatts.  To 
give  this  voltage  and  capacity,  eight  dynamos  are  connected  in  series  at 
the  generating  station,  each  dynamo  having  an  output  of  150  amperes  at 
i, 800  volts,  or  216  kilowatts. 

Continuous-current  motors  are,  of  course,  subject  to  the  same  limita- 
tions as  dynamos  in  the  matter  of  capacity  at  high  voltage,  so  that  a  series 


38      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

of  motors  must  be  employed  to  receive  the  high-pressure  energy  from  the 
line.  The  number  of  these  motors  may  just  equal,  or  may  be  less  or 
greater  than  the  number  of  dynamos,  but  the  total  working  voltage  of  all 
the  motors  in  operation  at  one  time  must  equal  the  total  voltage  of  the 
dynamos  in  operation  at  that  time  minus  the  volts  of  drop  in  the  line. 

Each  constant-current  motor  may  have  any  desired  capacity  up  to 
the  practicable  maximum,  but  it  must  be  designed  for  the  current  of  the 
system.  The  voltage  at  the  terminals  of  each  motor  varies  with  its  load, 
being  greatest  when  the  motor  is  doing  the  most  work.  Constant  speed 
is  usually  attained  at  each  motor  by  means  of  a  variable  resistance  con- 
nected across  the  terminals  of  the  magnet  coils.  The  amount  of  this  re- 
sistance is  regulated  by  a  centrifugal  governor,  driven  by  the  motor  shaft. 
This  governor  also  shifts  the  position  of  the  brushes  on  the  commutator 
to  prevent  sparking  as  the  current  flowing  through  the  magnet  coils  is 
changed. 

For  a  constant-current  transmission  the  magnet  and  armature  wind- 
ings of  both  dynamos  and  motors  are  usually  connected  in  series  with 
each  other  and  the  line  so  that  the  same  current  passes  through  every 
element  of  the  circuit,  except  that  each  motor  may  have  some  current 
shunted  out  of  its  magnet  coil  for  the  purpose  of  speed  regulation. 

In  some  cases,  however,  the  magnet  coils  of  the  dynamos  are  con- 
nected in  multiple  with  each  other  and  receive  their  current  from  a  sep- 
arate dynamo  designed  for  the  purpose.  With  this  separate  excitation 
of  the  magnet  coils,  the  dynamo  armatures  are  still  connected  in  series 
with  each  other  and  the  line. 

The  total  voltage  at  the  generating  station  and  on  the  line  af  a  con- 
stant-current system  varies  with  the  rate  at  which  energy  is  delivered,  and 
has  its  maximum  value  only  at  times  of  full  load.  To  obtain  this  varia- 
tion of  voltage,  it  is  the  general  practice  to  change  the  speed  of  the  dyna- 
mos by  means  of  an  automatic  regulator  which  is  actuated  by  the  line 
current.  Any  increase  of  the  line  current  actuates  the  regulator  and  re- 
duces the  speed  of  the  dynamos,  while  a  decrease  of  the  line  current 
raises  the  dynamo  speed.  With  a  good  regulator  the  variations  of  the 
line  current  are  only  slight.  Under  this  method  of  regulation  the  dyna- 
mos in  operation  have  a  substantially  constant  current  in  both  armature 
and  magnet  coils  at  all  times,  so  that  there  is  no  reason  to  shift  the  posi- 
tion of  the  brushes  on  the  commutator. 

Generating  stations  of  constant  current  transmission  systems  are 
generally  driven  by  water-power  and  the  speed  regulator  operates  to 
change  the  amount  of  water  admitted  to  each  wheel.  Each  turbine 


CONTINUOUS  AND  ALTERNATING  CURRENT.       39 

wheel  usually  drives  a  pair  of  dynamos,  but  one  or  any  number  of  dyna- 
mos might  be  driven  by  a  single  wheel.  The  two  dynamos  driven  by 
a  single  wheel  are  generally  connected  in  series  at  all  times,  and  are  cut 
in  or  out  of  the  main  circuit  together.  When  the  load  on  a  constant- 
current  generating  station  is  such  that  the  voltage  can  be  developed  by 
less  than  all  the  dynamos,  one  or  more  dynamos  may  be  stopped  and 
taken  out  of  the  circuit. 

To  do  this  the  dynamo  or  pair  of  dynamos  to  be  put  out  of  service 
may  be  stopped,  their  magnet  coils  having  first  been  short-circuited,  and 
then  a  switch  across  the  connections  of  their  armatures  to  the  lines 
closed,  after  which  the  connections  of  the  armatures  to  the  line  are 
opened.  By  a  reverse  process,  any  dynamo  or  pair  of  dynamos  may  be 
cut  into  the  operating  circuit. 

At  the  terminals  of  each  dynamo  in  the  series,  while  in  operation,  the 
voltage  is  simply  that  developed  in' its  armature,  so  that  the  insulation 
between  the  several  windings  is  subject  to  only  a  corresponding  stress. 
The  entire  voltage  of  the  line,  however,  tends  to  force  a  current  from  the 
coils  of  the  dynamo  at  one  end  of  the  series  into  its  frame,  thence  to  any 
substance  on  which  that  frame  rests,  and  so  on  to  the  frame  and  coils  of 
the  dynamo  at  the  other  end  of  the  series.  To  protect  the  insulation  of 
the  dynamo  coils  from  the  line  voltage,  thick  blocks  of  porcelain  are 
placed  beneath  the  dynamo  frames,  and  the  armature  shafts  are  con- 
nected to  those  of  the  turbines  by  insulating  couplings. 

Besides  the  switches,  already  mentioned,  a  voltmeter  and  ammeter 
should  be  provided  for  each  dynamo  and  also  for  the  entire  series  of 
machines.  This  completes  the  switchboard  equipment,  which  is,  there- 
fore, very  simple.  As  the  line  loss  of  a  constant-current  system  is  the 
same  whatever  the  load  that  is  being  operated,  this  loss  may  be  a  large 
percentage  of  the  total  output  when  the  load  is  light.  If,  for  illustration, 
five  per  cent  of  the  maximum  voltage  of  the  station  is  required  to  force 
the  constant  current  through  the  line,  the  percentage  of  line  loss  will 
rise  to  ten  when  the  station  voltage  is  one-half  the  maximum,  and 
to  twenty  when  the  station  is  delivering  only  one-quarter  of  its  full 
capacity. 

In  view  of  this  property  of  constant-current  working,  the  line  loss 
should  be  made  quite  small  in  its  ratio  to  the  maximum  load,  as  most 
stations  must  work  on  partial  loads  much  of  the  time.  Five  per  cent  of 
maximum  station  voltage  is  a  fair  general  figure  for  the  line  loss  in  a  con- 
stant-current transmission,  but  the  circumstances  of  a  particular  case 
may  dictate  a  higher  or  a  lower  percentage. 


40      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

On  the  32-mile  transmission,  above  named,  the  loss  in  the  line  is  six 
per  cent  of  the  station  output  at  full  load. 

If  a  transmission  with  continuous  current  is  to  be  carried  out  at  con- 
stant pressure  the  limitation  as  to  the  capacity  and  voltage  of  each  dy- 
namo is  about  the  same  as  with  constant  current.  Probably  more  energy 
is  now  transmitted  by  continuous  current  at  constant  pressure  than  by 
any  other  method,  the  greater  part  being  devoted  to  electric  railway  work 
at  500  to  600  volts.  Dynamos  for  about  these  voltages  can  readily  be 
had  in  capacities  up  to  several  thousand  kilowatts  each,  but  the  length 
of  transmission  that  can  be  economically  carried  out  at  this  pressure  is 
comparatively  small.  For  each  kilowatt  delivered  to  a  line  at  500  volts 
and  to  be  transmitted  to  a  distance  of  five  miles  at  a  ten  per  cent  loss  in 
the  line,  the  weight  of  copper  conductors  must  be  372  pounds,  costing 
#56.80  at  15  cents  per  pound.  This  sum  is  twice  to  four  times  the  cost 
of  good  continuous-current  dynamos  per  kilowatt  of  capacity.  If  the 
distance  of  transmission  is  ten  miles  and  the  voltage  and  line  loss  re- 
main as  before,  the  weight  of  copper  conductor  must  be  increased  to 
1,488  pounds  per  kilowatt  delivered  to  the  line,  costing  #227.20. 

Experience  has  shown  that  in  sizes  of  not  more  than  400  kilowatts, 
continuous-current  dynamos  may  safely  have  a  voltage  of  2,000  each, 
and  any  number  of  such  dynamos  may  be  operated  in  multiple,  giving 
whatever  capacity  is  desired.  At  2,000  volts  and  a  loss  of  10  per  cent 
in  the  line  the  weight  of  copper  conductors  per  kilowatt  would  be  93 
pounds,  costing  #13.95,  f°r  eacn  kilowatt  delivered  to  the  line  on  a  10- 
mile  transmission.  With  2,000  volts  on  a  2o-mile  transmission  the 
weight  of  conductors  per  kilowatt  would  be  the  same  as  their  weight  on 
a  5-mile  transmission  at  500  volts,  the  percentage  of  loss  being  equal  in 
the  two  cases.  Large  continuous-current  motors  of,  say,  50  kilowatts  or 
more  can  be  had  for  a  pressure  of  2,000  volts,  so  that  any  number  of 
such  motors  might  be  operated  from  a  2,000- volt,  constant-pressure  line 
entirely  independent  of  each  other.  From  these  figures  it  is  evident  that 
a  transmission  of  10  miles  may  be  carried  out  with  continuous-current  at 
constant  pressure  from  a  single  dynamo  with  good  efficiency  and  a  mod- 
erate investment  in  conductors. 

When  the  distance  is  such  that  much  more  than  2,000  volts  are  re- 
quired for  the  constant-pressure  transmission,  with  continuous  current, 
resort  must  be  had  to  the  connection  of  dynamos  and  motors  in  series. 
Any  number  of  dynamos  may  be  so  connected  as  in  the  case  of  constant- 
current  work.  The  combined  voltages  of  the  series  of  motors  connected 
to  the  constant-pressure  transmission  line  must  equal  the  voltage  of  that 


CONTINUOUS  AND  ALTERNATING  CURRENT.      41 

line,  so  that  the  number  of  motors  in  any  one  series  must  be  constant.  If 
the  voltage  of  transmission  is  so  high  that  more  than  two  or  three  motors 
must  be  connected  in  each  series,  there  comes  the  objection  that  motors 
must  be  operated  at  light  loads  during  much  of  the  time.  Moreover, 
each  series  of  motors  must  be  mechanically  connected  to  the  same  work, 
as  that  of  driving  a  single  dynamo  or  other  machine,  because  if  the  loads 
on  the  motors  of  a  series  vary  differently,  these  motors  will  not  operate 
at  constant  speed.  Continuous-current  transmission  at  constant  pres- 
sure with  motors  in  series  thus  lacks  the  flexibility  of  transmission  at 
constant  current  where  any  motor  may  be  started  and  stopped  without 
regard  to  the  others  in  the  series,  the  line  voltage  being  automatically 
regulated  at  the  generating  station  according  to  the  number  of  motors  in 
use  at  any  time  and  to  the  work  they  are  doing. 

In  the  efficiency  of  its  dynamos,  motors  and  line,  a  constant-pressure 
system  of  transmission  is  substantially  equal  to  one  with  constant  cur- 
rent at  full  load.  At  partial  loads  the  constant-pressure  line  has  the  ad- 
vantage because  the  loss  of  energy  in  it  varies  with  the  square  of  the  load. 
Thus  at  constant  pressure  the  line  loss  in  energy  per  hour  at  half -load  is 
only  one-fourth  as  great  as  the  loss  at  full  load.  On  the  other  hand,  the 
energy  loss  in  the  constant-current  line  is  the  same  at  all  stages  of  load. 
Because  of  these  facts  it  is  good  practice  to  allow,  say,  a  ten-per-cent  loss 
in  a  constant-pressure  line  and  only  five  per  cent  in  a  constant-current  line 
at  full  load. 

In  a  generating  station  at  2,000  volts  or  more  constant  pressure,  it  is 
desirable  to  have  the  magnet  coils  of  the  main  dynamos  connected  in 
multiple  and  separately  excited  by  a  small  dynamo  at  constant  pressure. 
This  plan  is  especially  desirable  when  the  armatures  of  several  dynamos 
are  connected  in  series  to  obtain  the  line  voltage.  Separately  excited 
magnet  coils  make  it  easier  to  control  the  operation  of  the  several  dy- 
namos, coils  of  low- voltage  are  cheaper  to  make  than  coils  of  high  voltage, 
and  the  low  voltage  windings  are  less  liable  to  burn  out.  If  a  series  of 
constant-pressure  motors  is  in  use  at  one  point,  it  may  be  cheaper  and 
safer  to  excite  its  magnet  coils  from  a  special  dynamo  than  from  the  line. 

In  a  transmission  carried  out  with  series- wound  dynamos  and  motors, 
the  speed  of  the  motors  may  be  constant  at  all  loads  without  any  special 
:egulating  mechanism.  To  attain  this  result  it  is  necessary  that  all  the 
motors  be  coupled  so  as  to  form  a  single  unit  mechanically  and  that  the 
dynamos  be  driven  at  constant  speed.  A  transmission  system  of  this 
sort  may  include  a  single  dynamo  and  a  single  motor,  or  two  or  more  dy- 
namos, and  two  or  more  motors  may  be  used  in  series. 


42      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

When  the  dynamos  of  such  a  system  are  driven  at  constant  speed  and 
a  variable  load  is  applied  to  the  single  motor,  or  to  the  mechanically  con- 
nected motors,  both  the  voltage  of  the  system  and  the  amperes  flowing 
in  all  its  parts  change  together  so  that  practically  constant  speed  is  main- 
tained at  the  motors,  provided  that  the  design  of  both  the  dynamos  and 
motors  is  suitable  for  the  purpose.  With  the  maximum  load  on  the 
motors  the  volts  and  amperes  of  the  system  have  their  greatest  values,  and 
these  values  both  decline  with  smaller  loads.  The  chief  disadvantage  of 
this  system  lies  in  the  fact  that  where  more  than  one  motor  is  employed 
all  the  motors  must  be  mechanically  joined  together  so  as  to  work  on 
the  same  load. 

Compared  with  the  constant-current  system,  this  combination  of 
series  dynamos  with  mechanically  connected  series  motors  has  the  dis- 
tinct advantage  that  neither  the  dynamos  nor  motors  require  any  sort  of 
regulators  in  order  to  maintain  constant  motor  speed.  It  is  only  neces- 
sary that  the  dynamos  be  driven  at  constant  speed  and  that  both  the  dy- 
namos and  motors  be  designed  for  the  transmission.  In  comparison  with 
a  constant-pressure  system,  the  one  under  consideration  has  the  advan- 
tage that  neither  its  dynamos  nor  motors  require  magnet  coils  with  a  high 
voltage  at  their  terminals  and  composed  of  fine  wire  or  separate  excita- 
tion by  a  special  dynamo.  These  features  of  the  system  with  series  dy- 
namos and  motors,  the  latter  being  joined  as  a  mechanical  unit,  make  it 
cheaper  to  install  and  easier  to  operate  than  either  of  the  other  two. 
This  system  is  especially  adapted  for  the  delivery  of  mechanical  power 
in  rather  large  units.  The  voltage  available  may  be  anything  desired, 
but  is  subject  to  the  practical  limitations  that  all  the  motors  must  deliver 
their  power  as  a  mechanical  unit,  so  that  unless  the  power  is  quite  large 
the  number  of  motors  in  the  series  and,  therefore,  the  voltage  is  limited. 

An  interesting  illustration  of  the  system  of  transmission  just  described 
exists  between  a  point  on  the  River  Suze,  near  Bienne,  Switzerland,  and 
the  Biberest  paper  mills.  At  the  river  a  400  horse-power  turbine  water- 
wheel  drives  a  pair  of  series- wound  dynamos,  each  rated  at  130  kilowatts 
and  3,300  volts.  These  dynamos  are  connected  in  series,  giving  a  total 
capacity  of  260  kilowatts  and  a  pressure  of  6,600  volts.  At  the  Biberest 
mills  are  located  two  series-wound  motors,  mechanically  coupled  and 
connected  in  series  with  each  other  and  with  the  two-wire  transmission 
line,  which  extends  from  the  two  dynamos  at  the  River  Suze.  Each  of 
these  motors  has  a  capacity  and  voltage  equal  to  that  of  either  of  the  dy- 
namos previously  mentioned.  The  coupled  motors  operate  at  the  con- 
stant speed  of  200  revolutions  per  minute  at  all  loads  and  deliver  over 


CONTINUOUS  AND  ALTERNATING  CURRENT.      43 

300  horse-power  when  doing  maximum  work.  Between  the  generating 
plant  at  the  river  and  the  Biberest  mills  the  distance  is  about  19  miles, 
and  the  two  line  wires  are  each  of  copper,  275  mils,  or  a  little  more 
than  one-fourth  inch  in  diameter.  The  dynamos  and  motors  of  this 
system  are  mounted  on  thick  porcelain  blocks  in  order  to  protect  the 
insulation  of  their  windings  from  the  strain  of  the  full-line  voltage. 

Either  of  the  three  systems  of  transmission  by  continuous-current  that 
have  been  considered  requires  a  smaller  total  capacity  of  electrical  appar- 
atus for  a  given  rate  of  mechanical  power  delivery  than  any  system  using 
alternating  current  except  that  where  both  the  dynamos  and  motors 
operate  at  line  voltage. 


CHAPTER  V. 

THE  PHYSICAL  LIMITS  OF  ELECTRIC-POWER  TRANSMISSION. 

ELECTRICAL  energy  may  be  transmitted  around  the  world  if  the  line 
voltage  is  unlimited.  This  follows  from  the  law  that  a  given  power  may 
be  transmitted  to  any  distance  with  constant  efficiency  and  a  fixed  weight 
of  conductors,  provided  the  voltage  is  increased  directly  with  the  dis- 
tance. 

The  physical  limits  of  electric-power  transmission  are  thus  fixed  by 
the  practicable  voltage  that  may  be  employed.  The  effects  of  the  voltage 
of  transmission  must  be  jnet  in  the  apparatus  at  generating  and  receiving 
stations  on  the  one  hand,  and  along  the  line  on  the  other.  In  both  situa- 
tions experience  is  the  main  guide,  and  theory  has  little  that  is  reliable 
to  offer  as  to  the  limit  beyond  which  the  voltage  will  prove  unworkable. 

Electric  generators  are  the  points  in  a  transmission  system  where  the 
limit  of  practical  voltage  is  first  reached.  In  almost  all  high-voltage 
transmissions  of  the  present  day  in  the  United  States  alternating  gene- 
rators are  employed.  Very  few  if  any  continuous-current  dynamos  with 
capacities  in  the  hundreds  of  kilowatts  and  voltages  above  4,000  have 
been  built  in  Europe,  and  probably  none  in  the  .United  States.  Where 
a  transmission  at  high  voltage  is  to  be  accomplished  with  continuous  cur- 
rent, two  or  more  dynamos  are  usually  joined  in  series  at  the  generating 
station,  and  a  similar  arrangement  with  motors  is  made  at  the  receiving 
station,  so  that  the  desired  voltage  is  available  at  the  line  though  not 
present  at  any  one  machine. 

Alternating  dynamos  that  deliver  current  at  about  6,000  volts  have 
been  in  regular  use  for  some  years,  in  capacities  of  hundreds  of  kilo- 
watts each,  and  may  readily  be  had  of  several  thousand  kilowatts 
capacity.  But  even  6,000  volts  is  not  an  economical  pressure  for  trans- 
missions over  fifteen  to  fifty  miles,  such  as  are  now  quite  common ;  conse- 
quently in  such  transmissions  it  has  been  the  rule  to  employ  alternators 
that  operate  at  less  than  3,000  volts,  and  to  raise  this  voltage  to  the  de- 
sired line  pressure  by  step-up  transformers  at  the  generating  station. 
More  recently,  however,  the  voltage  of  alternating  generators  has  been 
pushed  as  high  as  13,000  in  the  revolving-magnet  type  where  all  the  arma- 

44 


PHYSICAL  LIMITS  OF  TRANSMISSION.  45 

ture  windings  are  stationary.  This  voltage  makes  it  practicable  to  dis- 
pense with  the  use  of  step-up  transformers  for  transmissions  up  to  or 
even  beyond  30  miles  in  some  cases.  This  voltage  of  13,000  in  the  arma- 
ture coils  is  attained  only  by  constructions  involving  some  difficulty  be- 
cause of  the  relatively  large  amount  of  room  necessary  for  the  insulating 
materials  on  coils  that  develop  this  pressure.  The  tendency  of  this  con- 
struction is  to  give  alternators  unusually  large  dimensions  per  given  ca- 
pacity. It  seems  probable,  moreover,  that  the  pressures  developed  in  the 
armature  coils  of  alternating  generators  must  reach  their  higher  limits  at 
a  point  much  below  the  50,000  and  60,000  volts  in  actual  use  on  present 
transmission  lines.  In  the  longest  transmissions  with  alternating  current 
there  is,  therefore,  little  prospect  that  step-up  transformers  at  the  gen- 
erating stations  and  step-down  transformers  at  receiving  stations  can  be 
dispensed  with.  The  highest  voltage  that  may  be  received  or  delivered 
at  these  stations  is  simply  the  highest  that  it  is  practicable  to  develop  by 
transformers  and  to  transmit  by  the  line. 

A  very  high  degree  of  insulation  is  much  more  easy  to  attain  in  trans- 
formers than  in  generator  armatures,  because  the  space  that  can  be 
readily  made  available  for  insulating  materials  is  far  greater  in  the  trans- 
formers, and  further  because  their  construction  permits  the  complete 
immersion  of  their  coils  in  petroleum.  This  oil  offers  a  much  greater 
resistance  than  air  to  the  passage  of  electric  sparks,  which  tend  to  set  up 
arcs  between  coils  at  very  high  voltages  and  thus  destroy  the  insulation. 
Danger  to  insulation  from  the  effect  known  as  creeping  between  coils  at 
widely  different  pressures  is  largely  avoided  by  immersion  of  the  coils  in 
oil.  For  several  years  groups  of  transformers  have  been  worked  regu- 
larly at  40,000  to  60,000  volts,  and  in  no  instance  is  there  any  indica- 
tion that  the  upper  limit  of  practicable  voltage  has  been  reached.  On  the 
contrary,  transformers  have  repeatedly  been  worked  experimentally  up 
to  and  above  100,000  volts. 

From  all  these  facts,  and  others  of  similar  import,  it  is  fair  to  con- 
clude that  the  physical  limit  to  the  voltages  that  it  is  practicable  to  obtain 
with  transformers  is  much  above  the  50,000  or  6o,coo  volts  now  in  prac- 
tical use  on  transmission  systems.  So  far  as  present  practice  is  con- 
cerned, the  limit  to  the  use  of  high  voltages  must  be  sought  beyond  the 
transformers  and  outside  of  generating  and  receiving  stations.  As  now 
constructed,  the  line  is  that  part  of  the  transmission  system  where  a 
physical  limit  to  the  use  of  higher  voltages  will  first  be  reached.  The 
factors  that  tend  most  directly  to  this  limit  are  two:  temporary  arcing 
between  the  several  wires  on  a  pole,  and  the  less  imposing  but  constant 


46      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

passage  of  energy  from  one  wire  to  another.  On  lines  of  very  high  volt- 
age arcing  is  occasionally  set  up  by  one  of  several  causes.  At  a  point 
where  one  or  more  of  the  insulators  on  which  the  wires  are  mounted 
become  broken  or  defective,  the  current  is  apt  to  flow  from  one  wire 
to  another  along  a  wet  cross-arm,  until  the  wood  grows  carbonized  and 
an  arc  *is  formed  that  ends  by  burning  up  the  cross-arm  or  even  the  pole. 
Where  lines  are  exposed  to  heavy  sea  fog,  the  salt  is  in  some  cases  de- 
posited on  the  insulators  and  cross-arms  to  an  extent  that  starts  an  arc 
between  the  wires,  and  ends  often  in  the  destruction  of  the  cross-arm. 
In  some  instances  the  glass  and  porcelain  insulators  supporting  wires 
used  with  high  voltages  are  punctured  by  sparks  that  pass  right  through 
the  material  of  the  insulator  to  the  pin  on  which  it  is  mounted,  thus  burn- 
ing the  pin  and  ultimately  the  cross-arm.  This  trouble  is  easily  met, 
however,  by  the  adoption  of  a  better  grade  of  porcelain  or  of  an  insulator 
with  a  greater  thickness  of  glass  or  porcelain  between  the  wires  and  the 
supporting  pin.  Arcs  between  lines  at  high  voltages  usually  start  by 
sparks  that  jump  from  the  lower  edges  of  insulators,  when  they  are  wet 
or  covered  with  salt  deposit,  to  the  cross-arm.  As  the  lower  edges  of 
insulators  are  only  a  few  inches  from  their  cross-arms,  the  sparks  find  a 
path  of  comparatively  low  resistance  by  passing  from  insulator  to  cross- 
arm  and  thence  to  the  other  insulator  and  wire.  The  wood  of  a  wet 
cross-arm  is  a  far  better  conductor  than  the  air.  Where  wires  are  several 
feet  or  more  apart,  sparks  probably  never  jump  directly  through  the  air 
from  one  to  the  other.  Large  birds  flying  close  to  such  wires,  however, 
have  in  some  instances  started  momentary  arcs  between  them.  The 
treatment  of  cross-arms  with  oil  or  parafnne  reduces  the  number  of  arcs 
that  occur  on  a  line  of  high  voltage,  but  does  not  do  away  with  them. 

As  the  voltages  of  long  transmissions  have  gone  up,  the  distance 
through  the  air  between  wires  and  the  distances  between  the  lower  wet 
edges  of  insulators  and  the  cross-arms  have  been  much  increased.  Most 
of  the  earlier  transmission  lines  for  high  voltages  were  erected  on  insula- 
tors spaced  from  one  to  two  feet  apart.  In  contrast  with  this  practice, 
the  three  wires  of  the  transmission  line  in  operation  at  50,000  volts  be- 
tween Canon  Ferry  and  Butte  are  arranged  at  the  corners  of  a  triangle 
seventy-eight  inches  apart,  one  wire  at  the  top  of  each  pole  and  the  other 
two  at  opposite  ends  of  the  cross-arm.  A  voltage  that  would  just  start 
an  arc  along  a  wet  cross-arm  between  wires  eighteen  inches  apart  would 
be  quite  powerless  to  do  so  over  seventy-eight  inches  of  cross-arm,  the 
lower  wet  edges  of  insulators  being  equidistant  from  cross-arms  in  the 
two  cases.  To  reach  the  cross-arm,  the  electric  current  passes  down  over 


PHYSICAL  LIMITS  OF  TRANSMISSION.  47 

the  wet  or  dirty  outside  surface  of  the  insulator  to  its  lower  edge.  In  the 
older  types  of  insulators  the  lower  wet  edge  often  came  within  two  inches 
of  the  cross-arm.  For  the  5o,ooo-volt  line  just  mentioned  the  insulators 
(see  illus.)  are  mounted  with  their  lower  wet  edges  about  eight  inches 
above  the  cross-arms.  At  its  lower  edge  each  insulator  has  a  diameter 
of  nine  inches,  and  a  small  glass  sleeve  extends  several  inches  below  this 
edge  and  close  to  the  wooden  pin,  to  prevent  sparking  from  the  lower  wet 
edge  of  the  insulator  to  the  pin.  These  increased  distances  between 
wires  in  a  direct  line  through  the  air,  and  also  the  greater  distances  be- 
tween the  lower  wet  edges  of  insulators  and  their  pins  and  cross-arms,  are 
proving  fairly  effective  to  prevent  serious  arcing  under  good  climatic  con- 
ditions, for  the  maximum  pressures  of  50,000  to  60,000  volts  now  in  use. 
If  these  voltages  are  to  be  greatly  exceeded  it  is  practically  certain  that 
the  distance  between  wires,  and  from  the  lower  wet  edges  of  insulators  to 
the  wood  of  poles  or  cross-arms,  must  be  still  further  increased  to  avoid 
destructive  arcing. 

The  nearest  approach  to  an  absolute  physical  limit  of  voltage  with 
present  line  construction  is  met  in  the  constant  current  of  energy  through 
the  air  from  wire  to  wire  of  a  circuit.  A  paper  in  vol.  XV.,  Transac- 
tions American  Institute  Electrical  Engineers,  gives  the  tests  made  at 
Telluride,  Col.,  to  determine  the  rates  at  which  energy  is  lost  by  passing 
through  the  air  from  one  wire  to  another  of  the  same  circuit.  The  tests 
at  Telluride  were  made  with  two-wire  circuits  strung  on  a  pole  line 
11,720  feet  in  length,  at  first  with  iron  wires  of  0.165  inch  diameter  and 
then  with  copper  wires  of  0.162  inch  diameter.  Measurements  were 
made  of  the  energy  escaping  from  wire  to  wire  at  different  voltages  on 
the  line,  and  also  with  the  two  wires  at  various  distances  apart.  It  was 
found  that  the  loss  of  energy  over  the  surfaces  of  insulators  was  very 
slight,  and  that  the  loss  incident  to  the  passage  of  energy  directly  through 
the  air  is  the  main  one  to  be  considered.  This  leakage  through  the  air 
varies  with  the  length  of  the  line,  as  might  be  expected.  Tests  were 
made  with  pairs  of  wires  running  the  entire  length  of  the  pole  line  and 
at  distances  of  15,  22,  35,  and  52  inches  apart  respectively.  Losses 
with  wires  22  or  35  inches  apart  were  intermediate  to  the  losses  when 
wires  were  15  and  52  inches  apart  respectively.  Results  given  in  the 
original  paper  for  the  pair  of  wires  that  were  1 5  inches  apart  and  for  the 
pair  that  were  52  inches  apart  are  here  reduced  to  approximate  watts  per 
mile  of  two- wire  line.  At  40,000  volts  the  loss  between  the  two  wires  that 
were  1 5  inches  apart  was  about  1 50  watts  per  mile,  and  between  the  two 
wires  that  were  52  inches  apart  the  loss  was  84  watts  per  mile.  The  two 


48      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

wires  15  inches  apart  showed  a  leakage  of  approximately  413  watts  per 
mile  when  the  voltage  was  up  to  44,000,  but  the  wires  52  inches  apart 
were  subject  to  a  leakage  of  only  94  watts  per  mile  at  the  same  volt- 
age. At  47,300  volts,  the  highest  pressure  recorded  for  the  two  wires  15 
inches  apart,  the  leakage  between  them  was  about  1,215  watts  per  mile, 
while  an  equal  voltage  on  the  two  wires  52  inches  apart  caused  a  leakage 
of  only  122  watts  per  mile,  or  one-tenth  of  that  between  the  wires  that  were 
1 5  inches  apart.  When  about  50,000  volts  were  reached  on  the  two  wires 
52  inches  apart,  the  leakage  between  them  amounted  to  140  watts  per 
mile;  but  beyond  this  voltage  the  loss  went  up  rapidly,  and  was  225  watts 
per  mile  at  about  54,600  volts.  For  higher  pressures  the  loss  between 
these  two  wires  still  more  rapidly  increased,  and  amounted  to  1,368 
watts  per  mile  with  about  59,300  volts,  the  highest  pressure  re- 
corded. With  a  loss  of  about  1,215  watts  per  mile  between  the  two 
wires  52  inches  apart,  the  voltage  on  them  was  58,800,  in  contrast 
with  the  47,300  volts  producing  the  same  leakage  on  the  two  wires  15 
inches  apart. 

Evidently,  however,  at  even  52  inches  between  line  wires  the  limit  of 
high  voltage  is  not  far  away.  When  the  voltage  on  the  5  2 -inch  line  was 
raised  from  54,600  to  59,300,  the  leakage  loss  between  the  two  wires  in- 
creased about  1,143  watts  per  mile.  If  the  leakage  increases  at  least  in 
like  proportion,  as  seems  probable,  for  still  higher  pressures,  the  loss 
between  the  two  wires  would  amount  to  6,321  watts  per  mile  with  80,000 
volts  on  the  line.  On  a  line  200  miles  long  this  loss  by  leakage  between 
the  two  wires  would  amount  to  i  ,264,200  watts.  Any  such  leakage  as  this 
obviously  sets  an  absolute,  physical  limit  to  the  voltage,  and  consequently 
the  length  of  transmission. 

Fortunately  for  the  future  delivery  of  energy  at  great  distances  from 
its  source,  the  means  to  avoid  the  limit  just  discussed  are  not  difficult. 
Other  experiments  have  shown  that  with  a  given  voltage  and  distance 
between  conductors  the  loss  of  energy  from  wire  to  wire  decreases  rapidly 
as  their  diameters  increase.  The  electrical  resistance  of  air,  like  that  of 
any  other  substance,  increases  with  the  length  of  the  circuit  through  it. 
The  leakage  described  is  a  flow  of  electrical  energy  through  the  air  from 
one  wire  to  another  of  the  same  circuit.  To  reduce  this  leakage  it  is  sim- 
ply necessary  to  give  the  path  from  wire  to  wire  through  the  air  greater 
electrical  resistance  by  increasing  its  length,  that  is,  by  placing  the  wires 
at  greater  distances  apart.  The  fact  demonstrated  at  Telluride,  that  with 
47,300  volts  on  each  line  the  leakage  per  mile  between  the  two  wires  15 
inches  apart  was  ten  times  as  great  as  the  leakage  between  the  two  wires 


PHYSICAL  LIMITS  OF  TRANSMISSION.  49 

52  inches  apart,  is  full  of  meaning.  Evidently,  leakage  through  the  air 
may  be  reduced  to  any  desired  extent  by  suitable  increase  of  distance  be- 
tween the  wires  of  the  same  circuit.  But  to  carry  this  increase  of  distance 
between  wires  very  far  involves  radical  changes  in  line  construction. 
Thus  far  it  has  been  the  uniform  practice  to  carry  the  two  or  three  wires 
of  a  transmission  circuit  on  a  single  line  of  poles,  and  in  many  cases  sev- 
eral such  circuits  are  mounted  on  the  same  pole  line.  For  the  65  mile 
transmission  into  Butte,  Mont.,  only  the  three  wires  of  a  single  circuit  are 
mounted  on  one  pole  line,  and  this  represents  the  best  present  practice. 
The  cross-arms  on  this  line  are  each  8  feet  long,  and  one  is  attached  to 
each  pole.  The  poles  are  not  less  than  35  feet  long  and  have  8-inch  tops. 
One  wire  is  mounted  at  the  top  of  each  pole,  and  the  other  two  wires  near 
the  ends  of  the  cross-arm,  so  that  the  three  wires  are  equidistant  and  78 
inches  apart.  By  the  use  of  still  heavier  poles  the  length  of  cross-arms 
may  be  increased  to  12  or  14  feet,  for  which  their  section  should  be  not 
less  than  4  by  6  inches.  Placing  one  wire  at  the  pole  top,  the  1 2-foot 
cross-arm  would  permit  the  three  wires  of  a  circuit  to  be  spaced  about 
10.5  feet  apart.  The  cost  of  extra  large  poles  goes  up  rapidly  and  there 
are  alternative  constructions  that  seem  better  suited  to  the  case.  More- 
over, a  few  tens  of  thousands  of  volts  above  present  practice  would' bring 
us  again  to  a  point  where  even  10.5  feet  between  wires  would  not  prevent 
a  prohibitive  leakage.  Two  poles  might  be  set  20  feet  apart,  with  a 
cross-piece  between  them,  extending  out  5  feet  beyond  each  pole  and 
having  a  total  length  of  30  feet.  This  would  permit  three  wires  to  be 
mounted  along  the  cross-piece  at  points  about  14  feet  apart. 

If  the  present  transmission  pressures  of  50,000  to  60,000  volts  are  to 
be  greatly  exceeded,  the  line  structure  may  involve  the  use  of  a  sepa- 
rate pole  for  each  wire  of  a  circuit,  each  wire  to  be  mounted  at  the 
top  of  its  pole.  This  construction  calls  for  three  lines  of  poles  to  carry 
the  three  wires  of  a  three-phase  transmission.  Each  of  these  poles  may 
be  of  only  moderate  dimensions,  say  30  feet  long  with  6-  or  y-inch  top. 
The  cost  of  three  of  these  poles  will  exceed  by  only  a  moderate  percentage 
that  of  a  35-  or  40-foot  pole  with  an  8-  to  lo-inch  top,  such  as  would  be 
necessary  with  1 2-foot  cross-arms.  The  distance  between  these  poles  at 
right  angles  to  the  line  may  be  anything  desired,  so  that  leakage  from  wire 
to  wire  through  the  air  will  be  reduced  to  a  trifling  matter  at  any  voltage. 
Extra  long  pins  and  insulators  at  the  pole  tops  will  easily  give  a  distance 
of  two  feet  or  more  between  the  lower  wet  edge  of  each  insulator  and 
the  wood  of  pin  or  pole.  Such  line  construction  would  probably  safely 
carry  two  or  three  times  the  maximum  voltage  of  present  practice,  and 


50      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

might  force  the  physical  limit  of  electrical  transmission  back  to  the 
highest  pressure  at  which  transformers  could  be  operated.  With  not 
more  than  60,000  volts  on  the  line  the  size  of  conductors  is  great  enough 
in  many  cases  to  keep  the  loss  of  energy  between  them  within  moderate 
limits  when  they  are  six  feet  apart,  but  with  a  large  increase  of  voltage 
the  size  of  conductors  must  go  up  or  the  distances  between  them  must 
increase, 


CHAPTER  VI. 

DEVELOPMENT  OF  WATER-POWER  FOR  ELECTRIC  STATIONS. 

ELECTRICAL  transmission  has  reduced  the  cost  of  water-power  de- 
velopment. Without  transmission  the  power  must  be  developed  at  a 
number  of  different  points  in  order  that  there  may  be  room  enough  for 
the  buildings  in  which  it  is  to  be  utilized.  This  condition  necessitates 
relatively  long  canals  to  conduct  the  water  to  the  several  points  where 
power  is  to  be  developed,  and  also  a  relatively  large  area  of  land  with 
canal  and  river  frontage. 

With  electrical  transmission  the  power,  however  great,  may  well  be 
developed  at  a  single  spot  and  on  a  very  limited  area  of  land.  The  canal 
in  this  case  may  be  merely  a  short  passageway  from  one  end  of  a  dam  to 
a  near-by  power-house,  or  may  disappear  entirely  when  the  power-house 
itself  forms  the  dam,  as  is  sometimes  the  case. 

These  differences  between  the  distribution  of  water  for  power  pur- 
poses and  the  development  by  water  of  electrical  energy  for  transmission 
may  be  illustrated  by  many  examples. 

A  typical  case  of  the  distribution  of  water  to  the  points  where  power 
is  wanted  may  be  seen  in  the  hydraulic  development  of  the  Amcskeag 
Manufacturing  Company  at  Manchester,  N.  H.  This  development 
includes  a  dam  across  the  Merrimac  River,  and  two  parallel  canals 
that  follow  one  of  its  banks  for  about  3,400  feet  down  stream.  By  means 
of  a  stone  dam  and  a  natural  fall  a  little  beyond  its  toe  a  water  head  of 
about  forty-eight  feet  is  obtained  at  the  upper  end  of  the  high-level  canal. 
Below  this  point  there  is  little  drop  in  the  bed  of  the  river  through 
that  part  of  its  course  that  is  paralleled  by  the  two  canals.  All  of  the 
power  might  be  thus  developed  within  a  few  rods  of  one  end  of  the  dam, 
if  means  were  provided  for  its  distribution  to  the  points  where  it  must  be 
used. 

Years  ago,  when  this  water-power  was  developed,  the  electrical  trans- 
mission or  distribution  of  energy  was  unheard  of,  and  distribution  of  the 
water  itself  had  therefore  to  be  adopted.  For  this  purpose  the  two  canals 
already  mentioned  were  constructed  along  the  high  bank  of  the  river  at 
two  different  levels. 


ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


The  high-level  canal,  so  called, 
was  designed  to  take  water  di- 
rectly from  the  basin  or  forebay  a 
little  below  one  end  of  the  dam,  so 
that  between  this  canal  and  the 
river  there  is  a  full  water  head  of 
about  forty-eight  feet.  Over  nearly 
its  entire  course  the  nearer  side  of 
this  high-level  canal  runs  between 
450  and  7  50  feet  from  the  edge  of 
the  river  wall,  and  thus  includes 
between  it  and  the  river  a  large 
area  on  which  factories  to  be 
driven  by  water-wheels  may  be  lo- 
cated. It  was  thought,  however, 
that  this  strip  of  land  between  the 
high-level  canal  and  the  river  was 
too  wide  for  a  single  row  of  mill 
sites,  and  the  lower  level  canal 
was  therefore  constructed  parallel 
with  that  on  the  higher  level,  but 
with  about  twenty-one  feet  less 
elevation. 

Between  these  two  canals  a  strip 
of  land  about  250  feet  wide  was  left 
for  the  location  of  mills.  By  this 
arrangement  of  canals  it  is  possible 
to  supply  wheels  located  between 
the  high  and  the  low  levels  with 
water  under  a  head  of  about  twen- 
ty-one feet,  and  to  supply  wrheels 
between  the  lower  canal  and  the 
river  with  water  undei  a  head  of 
about  twenty-nine  feet.  The  en- 
tire area  of  land  between  the  high 
canal  and  the  river  is  thus  made 
readily  available  for  factory  build- 
ings. 

Water  for  the  lower  canal  is 
drawn  mainly  from  the  high  canal 


WATER-POWER  FOR  ELECTRIC  STATIONS.  53 

through  the  wheels  in  buildings  that  are  located  between  the  two  canals. 
It  is  desirable  in  a  case  of  this  sort  to  have  as  much  water  flow  through 
the  wheels  between  the  high  and  low  canal  as  flows  through  the  wheels 
between  the  low  canal  and  the  river,  but  this  is  not  always  possible.  A 
gate  is  therefore  provided  at  the  f orebay  where  the  two  canals  start,  by 
which  water  may  pass  from  the  forebay  directly  into  the  low  canal  when 
necessary,  but  the  head  of  twenty-one  feet  between  the  forebay  and  the 
low  canal  is  lost  as  to  this  water.  Between  the  high  and  low  canal,  and 
between  the  low  canal  and  the  river  twenty-three  turbine  wheels  or  pairs 
of  wheels  have  been  connected,  and  these  wheels  have  a  combined  rating 
of  9,500  horse-power. 

To  carry  out  this  hydraulic  development  it  thus  appears  that  about 
1.3  miles  of  canal  have  been  constructed;  one-half  this  length  of  river- 
front has  been  required,  and  about  one-sixth  square  mile  of  territory  has 
been  occupied.  Contrast  with  this  result  what  might  have  been  done  if 
electrical  transmission  of  power  had  been  available  at  the  time  when  this 
water-power  was  developed.  All  but  a  few  rods  in  length  of  the  existing 
1.3  miles  of  canal  might  have  been  omitted,  and  an  electric  generating 
station  with  wheels  to  take  the  entire  flow  of  the  river  might  have  been 
located  not  far  from  one  end  of  the  dam.  Factories  utilizing  the  electric 
power  thus  developed  might  have  been  located  at  any  convenient  points 
along  the  river-front  or  elsewhere,  and  no  space  would  have  been  made 
unavailable  because  of  the  necessity  of  head-  and  tail-water  connections 
to  scattered  sets  of  wheels. 

Compare  with  the  foregoing  hydraulic  development  that  at  Canon 
Ferry  on  the  Missouri  River,  in  Montana,  where  10,000  horse-power  is 
developed  under  a  water-head  of  32  feet.  At  Canon  Ferry  the  power- 
house is  225  feet  by  50  feet  at  the  floor  level  inside,  contains  turbine 
wheels  direct-connected  to  ten  main  generators  of  7,500  kilowatts,  or 
10,000  horse-power  combined  capacity,  and  is  built  on  the  river  bank 
close  to  one  end  of  the  5oo-foot  dam.  The  canal  which  runs  along  the 
land  side  of  the  power-house,  and  takes  water  at  the  up-stream  side  of 
the  abutment,  is  about  twice  the  length  of  the  power-house  itself.  The 
saving  in  the  cost  of  canal  construction  alone,  to  say  nothing  of  the  saving 
as  to  the  required  area  of  land,  is  evidently  a  large  item  in  favor  of  the 
electrical  development  and  transmission.  In  its  small  area  and  short 
canal  the  Canon  Ferry  plant  is  not  an  exception,  but  is  rather  typical  of 
a  large  class  of  electric  water-power  plants  that  operate  under  moderate 
heads. 

A  like  case  may  be  seen  in  the  plant  at  Red  Bridge,  on  the  Chicopee 


54      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

River,  in  Massachusetts,  where  a  canal  340  feet  long,  together  with  pen- 
stocks 100  feet  long,  convey  water  from  one  end  of  the  dam  and  deliver 
it  to  wheels  in  the  electric  station  with  a  head  of  49  feet.  This  station 
contains  electric  generators  with  a  combined  capacity  of  4,800  kilowatts 
or  6,400  horse-power,  and  its  floor  area  is  141  by  57  feet. 

So,  again,  at  Great  Falls,  on  the  Presumpscot  River,  in  North  Gor- 
ham,  Me.  (see  cut),  the  electric  station  sets  about  40  feet  in  front  of 


FIG.  5.— Canal  at  Red  Bridge  on  Chicopee  River. 

the  forebay  wall,  which  adjoins  one  abutment  of  the  dam,  and  there  is 
no  canal  whatever,  as  short  penstocks  bring  water  to  the  wheels  with  a 
head  of  35  feet.  In  ground  area  this  station  is  67.5  by  55  feet,  and  its 
capacity  in  main  generators  is  2,000  kilowatts  or  2,700  horse-power. 

A  striking  illustration  of  the  extent  to  which  electrical  transmission 
reduces  the  cost  of  water-power  development  may  be  seen  at  Gregg's 
Falls  on  the  Piscataquog  River,  in  New  Hampshire,  where  an  electric 
station  of  1,200  kilowatts  capacity  has  been  built  close  to  one  end  of  the 
dam,  and  receives  water  for  its  wheels  under  a  head  of  51  feet  through 
a  short  penstock,  10  feet  in  diameter,  that  pierces  one  of  the  abutments. 

Perhaps  the  greatest  electric  water-power  station  anywhere  that  rests 
close  to  the  dam  that  provides  the  head  for  its  wheels  is  that  at  Spier 


WATER-POWER  FOR  ELECTRIC  STATIONS.  55 


56      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Falls  (see  cut),  on  the  upper  Hudson.  One  end  of  this  station  is  formed 
by  the  high  wall  section  of  the  dam,  and  from  this  wall  the  length  of  the 
station  down-stream  is  392  feet,  while  its  width  is  70  feet  10  inches,  both 
dimensions  being  taken  inside.  The  canal  or  forebay  in  this  case,  like 
that  at  Canon  Ferry,  lies  on  the  bank  side  of  the  power-station,  and  is 
about  equal  to  it  in  length.  From  this  canal  ten  short  penstocks,  each 
1 2  feet  in  diameter,  will  convey  water  under  a  head  of  80  feet  to  as  many 
sets  of  turbine  wheels  in  the  station.  These  wheels  will  drive  ten  gen- 
erators with  an  aggregate  capacity  of  24,000  kilowatts  or  32,000  horse- 
power. 

Sometimes  the  slope  in  the  bed  of  a  river  is  so  gradual  or  so  divided 
up  between  the  number  of  small  falls,  or  the  volume  of  water  is  so  small, 
that  no  very  large  power  can  be  developed  at  any  one  point  without  the 
construction  of  a  long  canal.  In  a  case  of  this  sort  electrical  transmission 
is  again  available  to  reduce  the  expense  of  construction  that  will  make  it 
possible  to  concentrate  all  the  power  from  a  long  stretch  of  the  river  at  a 
single  point.  This  is  done  by  locating  electric  generating  stations  at  as 
many  points  as  may  be  thought  desirable  along  the  river  whose  energy  is 
to  be  utilized,  and  then  transmitting  power  from  all  of  these  stations  to 
the  single  point  where  it  is  wanted. 

A  case  in  point  is  that  of  Garvins  Falls  and  Hooksett  Falls  on  the 
Merrimac  River  and  four  miles  apart.  At  the  former  of  these  two  falls 
the  head  of  water  is  twenty-eight  feet,  and  at  the  latter  it  is  sixteen  feet. 
To  unite  the  power  of  both  these  falls  in  a  single  water-driven  station 
would  obviously  require  a  canal  four  miles  long  whose  expense  might  well 
be  prohibitive.  Energy  from  both  these  falls  is  made  available  at  a 
single  sub-station  in  Manchester,  N.  H.,  by  a  generating  plant  at  both 
points  and  transmission  lines  thence  to  that  city. 

At  Hooksett  the  present  capacity  of  the  electric  station  is  1,000  horse- 
power, and  at  Garvins  Falls  the  capacity  is  1,700  horse-power.  The 
river  is  capable  of  developing  larger  powers  at  both  of  these  falls,  how- 
ever, and  construction  is  now  under  way  at  Garvins  that  will  raise  its 
station  capacity  to  5,000  horse-power. 

A  similar  result  in  the  combination  of  water-powers  without  the  aid 
of  a  long  canal  is  reached  in  the  case  of  Gregg's  Falls  and  Kelley's  Falls, 
which  are  three  miles  apart  on  the  Piscataquog  River.  At  the  former  of 
these  two  falls  the  electric  generating  capacity  is  1,600  horse-power,  as 
previously  noted,  and  at  the  latter  fall  the  capacity  is  1,000  horse-power. 
In  each  case  the  station  is  close  to  its  dam,  and  no  canal  is  required. 
Electrical  transmission  unites  these  two  powers  in  the  same  sub-station 


WATER-POWER  FOR  ELECTRIC  STATIONS.  57 

at  Manchester  that  receives  the  energy  from  the  two  stations  above 
named  on  the  Merrimac  River. 

Instead  of  transmitting  power  from  two  or  more  waterfalls  to  some 
point  distant  from  each  of  them,  the  power  developed  at  one  or  more 
falls  may  be  transmitted  to  the  site  of  another  and  there  used.  This  is, 
in  fact,  done  at  the  extensive  Ludlow  twine  mills  on  the'Chicopee  River, 
in  Massachusetts.  These  mills  are  located  at  a  point  on  the  river  where 
its  fall  makes  about  2,500  horse-power  available,  and  this  fall  has  been 
developed  to  its  full  capacity.  After  a  capacity  of  2,400  horse-power  in 
steam-engines  had  been  added,  more  water-power  was  sought,  and  a  new 
dam  was  located  on  the  same  river  at  a  point  about  4.5  miles  up-stream 
from  the  mills.  The  entire  flow  of  the  river  was  available  at  this  new 
dam,  and  a  canal  4.5  miles  long  might  have  been  employed  to  carry  the 
water  down  to  wheels  at  the  mills  in  Ludlow. 

Such  a  canal  would  have  meant  a  large  investment,  not  only  for  land 
and  construction,  but  also,  possibly,  for  damages  to  estates  bordering  on 
the  river,  if  all  of  its  water  was  diverted.  Instead  of  such  a  canal,  an 
electric  generating  station  was  located  close  to  the  new  dam  with  a  capac- 
ity of  6,400  horse-power,  and  this  power  is  transmitted  to  motors  in  the 
mills  at  Ludlow. 

Even  where  the  power  is  to  be  utilized  at  some  point  distant  from  each 
of  several  waterfalls,  it  may  be  convenient  to  combine  the  power  of  all 
at  one  of  them  before  transmitting  it  to  the  place  of  use.  This  is  actually 
done  in  the  case  of  two  electric  stations  located  respectively  at  Indian 
Orchard  and  Birchem  Bend  on  the  Chicopee  River,  whose  energy  is  de- 
livered to  the  sub-station  of  the  electrical  supply  system  in  Springfield, 
Mass.  At  the  Indian  Orchard  station  the  head  of  water  is  36  feet, 
and  at  Birchem  Bend  it  is  14  feet,  while  the  two  stations  are  about  2 
miles  apart.  A  canal  of  this  length  might  have  been  built  to  give  a  head 
of  50  feet  at  the  site  of  the  Birchem  Bend  dam,  but  instead  of  this  an  elec- 
tric station  was  located  near  each  fall,  and  a  transmission  line  was  built 
between  the  two  stations.  Each  generating  station  was  also  connected 
with  the  sub-station  in  Springfield  by  an  independent  line,  and  power  is 
now  transmitted  from  one  generating  plant  to  the  other,  as  desired,  and 
the  power  of  both  may  go  to  the  sub-station  over  either  line.  In  the  In- 
dian Orchard  station  the  dynamo  capacity  is  about  2,000  kilowatts,  and 
at  Birchem  Bend  it  is  800  kilowatts. 

Another  case  showing  the  union  of  two  water-powers  by  electrical 
transmission,  where  the  construction  of  an  expensive  canal  was  avoided, 
is  that  of  the  electrical  supply  system  of  Hartford,  Conn.  This  sys- 


58      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

tern  draws  a  large  part  of  its  energy  from  two  electric  plants  on  the 
Farmington  River,  at  points  that  are  about  3  miles  apart  in  the  towns  of 
Windsor  and  East  Granby,  respectively.  At  one  of  these  plants  the  head 
of  water  is  32  feet,  and  at  the  other  it  is  23  feet,  so  that  head  of  55  feet 
might  have  been  obtained  by  building  a  canal  3  miles  long.  Each  of 
these  stations  is  located  near  its  dam,  and  the  generator  capacity  at  one 
station  is  1,200  and  at  the  other  1,500  kilowatts.  Transmission  lines 
deliver  power  from  both  of  these  plants  to  the  same  sub-station  in  Hart- 
ford. 

Sometimes  two  or  more  water-powers  on  the  same  river  that  are  to  be 
united  are  so  far  apart  that  any  attempt  to  construct  a  canal  between 
them  would  be  impracticable.  This  is  illustrated  by  the  Spier  and  Me- 
chanicsville  Falls  on  the  Hudson  River,  which  are  25  miles  apart  in  a 
direct  line  and  at  a  greater  distance  by  the  course  of  the  stream.  At  Spier 
Falls  the  head  is  80  feet,  and  at  Mechanicsville  it  is  1 8  feet.  Union  of  the 
power  of  these  two  falls  is  thus  out  of  the  question  for  physical  reasons 
alone.  Electrical  transmission,  however,  brings  energy  from  both  of 
these  water-powers  to  the  same  sub-stations  in  Schenectady,  Albany,  and 
Troy. 

In  another  class  of  cases  electrical  transmission  does  what  could  not 
be  done  by  any  system  of  canals,  however  expensive;  that  is,  unites  the 
water-powers  of  distinct  and  distant  rivers  at  any  desired  point.  Thus 
power  from  both  the  Merrimac  and  the  Piscataquog  rivers  is  distributed 
over  the  same  wires  in  Manchester;  the  Yuba  and  the  Mokelumne  con- 
tribute to  electrical  supply  along  the  streets  of  San  Francisco;  and  the 
Monte  Alto  and  Tlalnepantla  yield  energy  in  the  City  of  Mexico. 

It  does  not  follow  from  the  foregoing  that  it  is  always  more  economical 
to  develop  two  or  more  smaller  water-powers  at  different  points  along  a 
river  for  transmission  to  some  common  centre  than  it  is  to  concentrate 
the  water  at  a  single  larger  station  by  more  elaborate  hydraulic  construc- 
tion, and  then  deliver  all  of  the  energy  over  a  single  transmission  line. 
The  single  larger  hydraulic  and  electric  plant  will  usually  have  a  first 
cost  larger  than  that  of  the  several  smaller  ones,  because  of  the  re- 
quired canals  or  pipe  lines.  A  partial  offset  to  this  larger  hydraulic  in- 
vestment is  the  difference  in  cost  between  one  and  several  transmission 
lines,  or  at  least  the  cost  of  the  lines  that  would  be  necessary  between  the 
several  smaller  stations  in  order  to  combine  their  energy  output  before 
its  transmission  over  a  single  line  to  the  point  of  use. 

Against  the  total  excess  of  cost  for  the  single  larger  hydraulic  and 
electrical  plant  there  should  be  set  the  greater  expense  of  operation  at 


WATER-POWER  FOR  ELECTRIC  STATIONS.  59 

several  smaller  and  separate  plants.  Even  a  small  water-driven  electric 
station  that  can  be  operated  by  a  single  attendant  at  any  one  time  must 
have  two  attendants  if  it  is  to  deliver  energy  during  the  greater  part  or  all 
of  every  twenty-four  hours.  But  a  single  attendant  can  care  for  a  water- 
power  plant  of  2, ocx)  horse-power  or  more  capacity,  so  that  two  plants  of 
750  horse-power  each  will  require  double  the  operating  force  of  one  plant 
of  1,500  horse-power.  If  two  such  plants  are  constructed  instead  of  one 
that  has  their  combined  capacity,  the  monthly  wages  of  the  two  addi- 
tional operators  will  amount  to  at  least  one  hundred  dollars.  If  money 
is  worth  six  per  cent  yearly,  it  follows  that  an  additional  investment  of 
#1,200  -:-  0.06  =1  $20,000  might  be  made  in  hydraulic  work  to  concen- 
trate the  power  at  one  point  before  the  annual  interest  charge  would  equal 
the  increase  of  wages  made  necessary  by  two  plants. 

Reliability  of  operation  is  one  of  the  most  important  requirements  in 
an  electric  water-power  plant,  and  its  construction  should  be  carried  out 
with  this  in  view.  Anchor  ice  is  a  serious  menace  to  the  regular  opera- 
tion of  water-wheels  in  cold  climates,  because  it  clogs  up  the  openings  in 
the  racks  and  in  the  wheel  passages.  Anchor  ice  is  formed  in  small 
particles  in  the  water  of  shallow  and  fast-flowing  streams,  and  tends  to 
form  into  masses  on  solid  substances  with  which  the  water  comes  in  con- 
tact. 

At  the  entrance  to  penstocks  or  wheel  chambers,  steel  racks  with  long, 
narrow  openings,  say  one  and  one-quarter  inches  wide,  are  regularly 
placed  to  keep  all  floating  objects  away  from  the  wheels.  When  water 
bearing  fine  anchor  or  frazil  ice  comes  in  contact  with  these  racks,  it  rap- 
idly clogs  up  the  narrow  openings  between  the  bars,  unless  men  are  kept 
at  work  raking  off  the  ice  as  it  forms.  At  the  Niagara  Falls  electric 
station,  in  some  instances,  when  the  racks  become  clogged,  they  have 
been  lifted,  and  the  anchor  ice  allowed  to  pass  down  through  the  wheels. 
This  is  said  to  have  proved  an  effective  remedy,  but  it  would  obviously 
be  of  no  avail  in  a  case  where  the  ice  clogged  the  passages  of  the  wheels 
themselves. 

The  best  safeguard  against  anchor  ice  is  a  large,  deep  forebay  next 
to  the  racks,  where  the  water,  being  comparatively  quiet,  will  soon  freeze 
over  after  cold  weather  commences.  The  anchor  ice  coming  down  to 
this  forebay  and  losing  most  of  its  forward  motion,  soon  rises  to  the  sur- 
face or  to  the  under  side  of  the  top  coating  of  solid  ice,  and  the  warmer 
water  sinks  to  the  bottom.  Good  construction  puts  the  entrance  ends 
of  penstocks  well  below  the  surface  of  water  in  the  forebay,  so  that  they 
may  receive  the  warmer  water  that  contains  little  or  no  anchor  ice. 


60      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Illustrations  of  practice  along  these  lines,  as  to  size,  depth  of  forebay, 
and  location  of  penstocks  may  be  seen  in  many  well-designed  plants. 
One  instance  is  that  at  Garvins  Falls,  on  the  Merrimac  River,  where  the 
new  hydraulic  development  for  5,000  horse-power  is  now  under  way. 
Water  from  the  river  in  this  case  comes  down  to  the  power-station  through 


El.  9i.OOF.ooJ  Water 


FIG.  7.— Cross  Section  of  Dike  on  Chicopee  River  at  Red  Bridge. 

a  canal  500  feet  long,  and  of  68  feet  average  width  midway  between  the 
bottom  and  the  normal  flow  line.  In  depth  up  to  his  flow  line  the  canal 
is  12  feet  at  its  upper  and  13  feet  at  its  lower  end,  just  before  it  widens 
into  the  forebay.  In  this  forebay  the  depth  increases  to  1 7  feet,  and  the 
width  at  the  rack  is  double  that  of  the  canal.  The  steel  penstocks,  each 
1 2  feet  in  diameter,  terminate  in  the  forebay  wall  at  an  average  distance 
of  7  feet  behind  the  rack,  and  each  penstock  has  its  centre  10.6  feet  below 
the  water  level  in  the  forebay.  As  there  is  a  large  pond  created  by  the 
dam  in  this  case,  and  as  the  flow  of  water  in  the  canal  is  deep  rather  than 
swift,  enough  opportunity  is  probably  afforded  for  any  anchor  ice  to  rise 
to  the  surface  before  it  reaches  the  forebay  in  this  case. 

Penstocks  for  the  electric  station  at  Great  Falls,  on  the  Presumpscot 
River,  whence  energy  is  drawn  for  lighting  and  power  in  Portland,  Me., 
are  each  8  feet  in  diameter,  and  pierce  the  forebay  wall  behind  the  rack 
with  their  centres  15  feet  below  the  normal  water  level  in  the  forebay. 
In  front  of  the  forebay  wall  the  water  stands  27  feet  deep,  and  the  pond 
formed  by  the  dam,  of  which  the  forebay  wall  forms  one  section,  is  1,000 
feet  wide  and  very  quiet.  Though  the  Maine  climate  is  very  cold  in 
winter  and  the  Presumpscot  is  a  turbulent  stream  above  the  dam  and 
pond,  there  has  never  been  any  trouble  with  anchor  ice  at  the  Great  Falls 
plant.  An  excellent  illustration  is  thus  presented  of  the  fact  that  deep, 
still  water  in  the  forebay  is  a  remedy  for  troubles  with  ice  of  this  sort. 

Maximum  loads  on  electrical  supply  systems  are  usually  from  twice 
to  four  times  as  great  as  the  average  loads  during  each  twenty-four  hours. 


WATER-POWER  FOR  ELECTRIC  STATIONS. 


61 


A  pure  lighting  service  tends  toward  the  larger  ratio  between  the  average 
and  maximum  load,  while  a  larger  motor  capacity  along  with  the  lamps, 
tends  to  reduce  the  ratio.  Furthermore,  by  far  the  greater  part  of  the 
energy  output  of  an  electrical  supply  system  during  each  twenty-four 
hours  must  be  delivered  between  noon  and  midnight.  For  these  reasons 
there  must  be  enough  water  stored,  that  can  flow  to  the  station  as  wanted, 
to  carry  a  large  share  of  the  load  during  each  day,  unless  storage  bat- 
teries are  employed  to  absorb  energy  at  times  of  light  load,  if  the  entire 
normal  flow  of  the  river  is  to  be  utilized. 

It  is  usually  much  cheaper  to  store  water  than  electrical  energy  for 
the  daily  fluctuations  of  load,  and  the  only  practicable  place  for  this  stor- 
age is  most  commonly  behind  the  dam  that  maintains  the  head  for  the 
power-station.  This  storage  space  should  be  so  large  that  the  drain  upon 


FIG.  8. -Valley  Flooded  above  Spier  Falls  on  the  Hudson  River. 

it  during  the  hours  of  heavy  load  will  lower  the  head  of  water  on  the 
wheels  but  little,  else  it  may  be  hard  to  maintain  the  standard  speed 
of  revolution  for  the  wheels  and  generators,  and  consequently  the  trans- 
mission voltage. 

At  the  Great  Falls  plant,  water  storage  to  provide  for  the  fluctuations 
of  load  in  different  parts  of  the  day  takes  place  back  of  the  dam,  and  for 


62      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

about  one  mile  up-stream.  This  dam  is  450  feet  long  in  its  main  part, 
and  a  retaining  wall  increases  the  total  length  to  about  i  ,000  feet.  For 
half  a  mile  up-stream  from  this  dike  and  dam  the  average  width  of  the 
pond  is  1,000  feet,  and  its  greatest  depth  is  not  less  than  27  feet.  As  the 
station  capacity  is  2,700  horse-power  in  main  generators,  with  a  head  of 
35  feet  at  the  wheels  the  storage  capacity  is  more  than  ample  for  all 
changes  of  load  at  different  times  of  day. 

The  dam  at  Spier  Falls,  on  the  Hudson  River,  it  1,820  feet  long  be- 
tween banks,  155  feet  high  above  bedrock  in  its  deepest  section,  and  raises 
the  river  50  feet  above  its  former  level.  Behind  the  dam  a  lake  is  formed 
one-third  of  a  mile  wide  and  5  miles  long.  Water  from  this  storage  reser- 
voir passes  down  through  the  turbines  with  a  head  of  80  feet,  and  is  to 
develop  32,000  horse-power.  As  a  little  calculation  will  show,  this  lake 
is  ample  to  maintain  the  head  under  any  fluctuation  in  the  daily  load. 
At  Canon  Ferry,  where  electrical  energy  for  Butte  and  Helena,  Mont., 
is  developed,  the  dam,  which  is  480  feet  long,  crosses  the  river  in  a  narrow 
canyon  that  extends  up-stream  for  about  half  a  mile.  Above  this  canyon 
the  river  valley  widens  out,  and  the  dam,  which  maintains  a  head  of  30 
feet  at  the  power-station,  sets  back  the  water  in  this  valley,  and  thus  forms 
a  lake  between  two  and  three  miles  wide  and  about  seven  miles  long. 
At  the  station  the  generator  equipment  has  a  total  rating  of  10,000  horse- 
power. From  these  figures  it  may  be  seen  that  the  storage  lake  would 
be  able  to  maintain  nearly  the  normal  head  of  water  for  some  hours,  when 
the  station  was  operating  under  full  load,  however  small  the  flow  of  the 
river  above. 


WATER-POWER  FOR  ELECTRIC  STATIONS. 


CHAPTER  VII. 

THE  LOCATION  OF  ELECTRIC  WATER-POWER  STATIONS. 

COST  of  water-power  development  depends,  in  large  measure,  on  the 
location  of  the  electric  station  that  is  to  be  operated.  The  form  of  such 
a  station,  its  cost,  and  the  type  of  generating  apparatus  to  be  employed 
are  also  much  influenced  by  the  site  selected  for  it.  This  site  may  be 
exactly  at,  or  far  removed  from,  the  point  where  water  that  is  to  pass 
through  the  wheels  is  diverted  from  its  natural  course. 

A  unique  example  of  a  location  of  the  former  kind  is  to  be  found  near 
Burlington,  Vt,  where  the  electric  station  is  itself  a  dam,  being  built 
entirely  across  the  natural  bed  of  one  arm  of  the  Winooski  River  at  a 
point  where  an  island  near  its  centre  divides  the  stream  into  two  parts. 
The  river  at  this  point  has  cut  its  way  down  through  solid  rock,  leaving 
perpendicular  walls  on  either  side.  Up  from  the  ledge  that  forms  the  bed 
of  the  stream,  and  into  the  rocky  walls,  the  power-station,  about  no  feet 
long,  is  built.  The  up-stream  wall  of  this  station  is  built  after  the  fashion 
of  a  dam,  and  is  reenforced  by  the  down-stream  wall,  and  the  water  flows 
directly  through  the  power-station  by  way  of  the  wheels.  A  construction 
of  this  sort  is  all  that  could  well  be  attained  in  the  way  of  economy,  there 
being  neither  canal  nor  long  penstocks,  and  only  one  wall  of  a  power-house 
apart  from  the  dam.  On  the  other  hand,  the  location  of  a  station  directly 
across  the  bed  of  a  river  in  this  way  makes  it  impossible  to  protect  the 
machinery  if  the  up-stream  wall,  which  acts  as  the  dam,  should  ever 
give  way.  The  peculiar  natural  conditions  favorable  to  the  construction 
just  considered  are  seldom  found. 

One  of  the  most  common  locations  for  an  electric  water-power  station 
is  at  one  side  of  a  river,  directly  in  front  of  one  end  of  the  dam  and  close 
to  the  foot  of  the  falls.  A  location  of  this  kind  was  adopted  for  the  station 
at  Gregg's  Falls,  one  of  the  water-powers  included  in  the  electric  system 
of  Manchester,  N.  H.,  where  the  spray  of  the  fall  rises  over  the  roof  of  the 
station.  Two  short  steel  penstocks,  each  ten  feet  in  diameter,  convey  the 
water  from  the  forebay  section  of  the  dam  to  wheels  in  the  station  with  a 
head  of  fifty-one  feet. 

A  similar  location  was  selected  for  the  station  at  Great  Falls,  on  the 

64 


LOCATION  OF  WATER-POWER  STATIONS. 


66      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


I 


LOCATION  OF  WATER-POWER  STATIONS. 


67 


Presumpscot  River  (see  cuts),  whence  electrical  energy  is  delivered  in 
Portland,  Me.  Four  steel  penstocks,  a  few  feet  long  and  each  eight  feet 
in  diameter,  bring  the  water  in  this  case  from  the  forebay  section  of  the 
dam  to  the  wheel  cases  in  the  power-house. 

Where  the  power-station  is  located  at  the  foot  of  the  dam,  as  just 
described,  that  part  which  serves  as  a  forebay  wall  usually  carries  a  head 
gate  for  each  penstock.  The  overfall  section  of  a  dam  may  give  way  in 


F 


FIG.  12.— Power-house  on  Hudson  River  at  Mechanicsville. 

cases  like  the  two  just  noted  without  necessarily  destroying  the  power- 
station,  but  in  times  of  freshet  or  very  high  water  the  station  may  be 
flooded  and  its  operation  stopped.  The  risk  of  any  such  flooding  will 
vary  greatly  on  different  rivers,  and  in  particular  cases  may  be'  very 
slight.  Location  of  the  generating  station  close  to  the  foot  of  the  dam 
at  one  end  obviously  avoids  all  expense  for  a  canal  and  cuts  the  cost  of 
penstocks  down  to  a  very  low  figure. 

Such  locations  for  stations  are  not  limited  to  falls  of  any  particular 
height,  and  the  short  penstocks  usually  enter  the  dam  nearer  its  base  than 
its  top  and  pass  to  the  station  at  only  a  slight  inclination  from  the  horizon- 
tal. At  Great  Falls,  above  mentioned,  the  head  of  water  is  thirty-seven 
feet. 

A  short  canal  is  constructed  in  some  cases  from  one  end  of  a  dam  to 
a  little  distance  down-stream,  terminating  at  a  favorable  site  for  the  elec- 
tric station.  Construction  of  this  sort  was  adopted  at  the  Birchem  Bend 
Falls  of  the  Chicopee  River,  whence  energy  is  supplied  to  Springfield, 
Mass.  These  falls  furnish  a  head  of  fourteen  feet,  and  the  water-wheels 
are  located  on  the  floor  of  the  open  canal  at  its  end.  The  power-station 
is  on  the  shore  side  of  this  canal,  and  the  shafts  of  the  water-wheels  extend 
through  bushings  in  the  canal  wall,  which  forms  the  lower  part  of  one 
side  of  the  station,  to  connect  with  the  electric  generators  inside. 


68      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

This  rather  unusual  location  of  water-wheels  has  at  least  the  obvious 
advantage  that  they  require  no  room  inside  of  the  station.  Furthermore, 
as  the  canal  is  between  the  station  and  the  river,  any  break  in  the  canal 
is  not  apt  to  flood  the  station. 

An  illustration  of  the  use  of  a  very  short  canal  to  convey  water  from 
one  end  of  a  dam  to  a  power-station  exists  in  the  10,000  horse-power 
plant  at  Canon  Ferry,  Mont.,  where  the  head  of  water  is  thirty  feet.  In 
this  case  the  masonry  canal  is  but  little  longer  than  the  power-house,  and 
this  latter  sits  squarely  between  the  canal  and  the  river,  virtually  at  the 


-    FIG.  13.— York  Haven  Power-house,  on  Susquehanna  River,  Pennsylvania. 

foot  of  the  falls.  Other  examples  of  the  location  of  generating  stations 
between  short  canals  and  the  river  may  be  seen  at  Concord,  N.  H.,  where 
the  head  of  water  is  sixteen  feet;  at  Lewiston,  Me.,  where  the  head  is 
thirty-two  feet;  and  at  Spier  Falls,  on  the  Hudson  River,  New  York, 
where  there  is  a  head  of  eighty  feet. 

There  is  some  gain  in  security  in  many  cases  by  locating  the  power- 
station  several  hundred  feet  from  the  dam  and  a  little  to  one  side  of  the 
main  river  channel.  For  such  cases  a  canal  may  be  cheaper  than  steel 
penstocks  when  the  items  of  depreciation  and  repairs  are  taken  into  ac- 
count. Aside  from  the  question  of  greater  security  for  the  station  in  the 
event  of  a  break  in  the  dam,  it  is  necessary  in  many  cases  to  convey  the 
water  a  large  fraction  of  a  mile,  or  even  a  number  of  miles,  from  the  point 
where  it  leaves  its  natural  course  to  that  where  the  power-station  should 
be  located.  An  example  in  point  exists  at  Springfield,  Mass.,  where 
one  of  the  electric  water-power  stations  is  located  about  1,400  feet  down- 
stream from  a  fall  of  thirty-six  feet  in  the  Chicopee  River,  because  land 
close  to  the  falls  was  all  occupied  at  the  time  the  electric  station  was  built. 


LOCATION  OF  WATER-POWER  STATIONS.  69 


70      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


LOCATION  OF  WATER-POWER  STATIONS.  71 

The  Shawinigan  Falls  of  the  St.  Maurice  River  in  Canada  occur  at 
two  points  a  short  distance  apart,  the  fall  at  one  point  being  about  50  and 
at  the  other  100  feet  high.  A  canal  1,000  feet  long  takes  water  from  the 
river  above  the  upper  of  these  falls  and  delivers  it  near  to  the  electric 
power-house  on  the  river  bank  below  the  lower  falls.  In  this  way  a  head 
of  125  feet  is  obtained  at  the  power-house.  The  canal  in  this  case  ends 
on  high  ground  130  feet  from  the  power-house,  and  the  water  passes  down 
to  the  wheels  through  steel  penstocks  9  feet  in  diameter. 

Another  interesting  example  of  conditions  that  require  a  power-house 
to  be  located  some  distance  from  the  point  where  water  is  diverted  from 
its  natural  course  may  be  seen  at  the  falls  on  the  Apple  River,  whence 


FIG  16. — Power-house  on  White  River,  Oregon. 

energy  is  transmitted  to  St.  Paul,  Minn.  By  means  of  a  natural  fall  of 
30  feet,  a  dam  47  feet  high  some  distance  up-stream,  and  some  rapids  in 
the  river,  it  was  there  possible  to  obtain  a  total  fall  of  82  feet.  To  utilize 
this  entire  fall  a  timber  flume,  1,550  feet  in  length,  was  built  from  the  dam 
to  a  point  near  the  power-house  on  the  river  bank  and  below  the  falls  and 
rapids.  The  flume  was  connected  with  the  wheels,  82  feet  below,  by  a 
steel  penstock  313  feet  long  and  12  feet  in  diameter. 

As  the  St.  Mary's  River  leaves  Lake  Superior  it  passes  over  a  series 
of  rapids  about  half  a  mile  in  length,  falling  twenty  feet  in  that  distance. 
To  make  the  power  of  this  great  volume  of  water  available,  a  canal  13,000 
feet  long  was  excavated  from  the  lake  to  a  point  on  the  river  bank  below 
the  rapids.  Between  the  end  of  the  canal  and  the  river  sits  the  power- 
station,  acting  as  a  dam,  and  the  water  passes  down  through  it  and  the 
wheels  under  a  head  of  twenty  feet. 


72      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


LOCATION  OF  WATER-POWER  STATIONS. 


73 


By  means  of  a  canal  16,200  feet  long  from  the  St.  Lawrence  River 
a  head  of  water  amounting  to  fifty  feet  has  been  made  available  at  a 
point  on  the  bank  of  Grass  River  near  Massena,  N.  Y.  There  again  the 
power-station  acts  as  a  dam,  and  the  canal  water  passes  down  through  it 
to  reach  the  river. 

From  these  illustrations  it  may  be  seen  that  in  many  cases,  in  com- 
paratively level  country,  a  water-power  can  be  fully  developed  only  by 


FIG.  iS.— Canal  and  Station  on  Payette  River,  Idaho. 


means  of  canals  or  pipe  lines,  and  the  generating  stations  cannot  be  lo- 
cated at  the  points  where  the  water  is  diverted. 

Thus  far  the  cases  considered  have  been  only  those  with  moderate 
heads  and  rather  large  volumes  of  water.  In  mountainous  country, 
where  rivers  are  comparatively  small  and  their  courses  are  marked  by 
numerous  falls  and  rapids,  it  is  generally  necessary  to  utilize  the  fall  of 
a  stream  through  some  miles  of  its  length  in  order  t&  effect  a  satisfactory 
development  of  power.  To  reach  this  result,  rather  long  canals,  flumes, 
or  pipe  lines  must  be  utilized  to  convey  the  water  to  power-stations  and 
deliver  it  at  high  pressures. 

In  cases  of  this  kind  the  cost  of  the  canal  or  pipe  line  may  be  the  larg- 
est item  in  the  power  development,  and  it  may  be  an  important  question 
whether  this  cost  should  be  reduced  or  avoided  by  the  erection  of  several 


74      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

small  generating  plants  instead  of  one  large  one.  California  offers  nu- 
merous examples  of  electric-power  development  with  water  that  has  been 
carried  several  miles  through  artificial  channels.  An  illustration  of  this 
class  of  work  exists  at  the  Electra  power-house  on  the  bank  of  the  Mo- 
kelumne  River,  in  the  Sierra  Nevada  Mountains.  Water  is  supplied  to 
the  wheels  in  this  station  under  a  head  of  1,450  feet  through  pipes  3,600 
feet  long  leading  to  the  top  of  a  near-by  hill.  To  reach  this  hill  the  water, 
after  its  diversion  from  the  Mokelumne  River  at  the  dam,  flows  twenty 
miles  through  a  canal  or  ditch  and  then  through  3,000  feet  of  wooden  stave 
pipe. 

Another  example  of  the  same  sort  may  be  seen  in  the  power-house  at 
Colgate,  on  the  North  Yuba  River,  in  the  chain  of  mountains  above 
named.  Water  taken  from  this  river  passes  through  a  wooden  flume 
nearly  eight  miles  long  to  the  side  of  a  hill  700  feet  above  the  power- 
house, and  thence  down  to  the  wheels  through  steel  and  cast-iron  pipes, 
five  in  number  and  thirty  inches  each  in  diameter. 

Even  with  long  flumes,  canals,  and  pipe  lines,  it  may  be  necessary 
to  locate  a  number  of  generating  stations  along  a  single  river  of  the 
class  now  under  consideration  in  order  to  utilize  its  entire  power. 
Thus  on  the  Kern  River,  which  rises  in  the  Sierra  Nevada  Mountains 
'and  empties  into  Tulare  Lake,  two  electric  power-stations  are  under 
construction,  and  surveys  are  being  made  for  three  more.  Of  these 
stations,  the  one  at  the  lowest  level  will  operate  under  an  872-foot  head 
of  water,  and  this  water,  after  its  diversion  from  the  river,  will  pass 
through  twenty-one  tunnels,  with  an  aggregate  length  of  about  ten 
miles,  and  through  six  flumes  mounted  on  trestles  and  having  a  total 
length  of  1,703  feet. 

Next  up-stream  is  a  station  near  the  point  where  water  is  diverted  for 
the  plant  just  named.  This  second  station  will  work  under  a  head  of 
317  feet,  and  water  for  it  will  come  from  a  point  farther  up-stream  by 
canals,  tunnels,  and  flumes,  with  an  aggregate  length  of  eleven  and  one- 
half  miles.  At  three  points  still  higher  up  on  this  river  it  is  the  intention 
to  locate  three  other  power-stations  by  conducting  the  water  in  artificial 
channels,  about  twelve  and  one-half,  fifteen,  and  twenty  miles  in  length 
respectively. 

Farther  south  in  California,  on  the  Santa  Ana  River  and  Mill  Creek, 
extensive  power  developments  on  the  lines  just  indicated  have  been  car- 
ried out.  On  Mill  Creek,  about  six  miles  from  the  city  of  Redlands,  is 
an  electric  station  operating  under  a  head  of  530  feet,  with  water  in  part 
diverted  from  the  stream  a  little  less  than  two  miles  above  and  brought 


LOCATION  OF  WATER-POWER  STATIONS.  75 


FIG.  19.— Canal  and  Power-station  on  Neversink  River,  New  York. 


76       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

down  through  a  steel  pipe  10,250  feet  long  and  thirty  inches  in  diame- 
ter. This  pipe  line  also  takes  water  from  the  tail  race  of  another  gener- 
ating plant  at  its  upper  end.  With  some  additions  and  modifications, 
the  station  just  described  is  the  famous  Redlands  plant,  built  in  1893, 
and  believed  to  be  the  first  for  three-phase  transmission  in  the  United 
States. 

At  the  upper  end  of  the  pipe  line  just  named  the  second  station  oper- 
ates, in  part,  with  water  drawn  from  Mill  Creek  through  a  combination 
of  tunnels,  flumes,  and  cement  and  steel  pipes,  with  a  combined  length 
of  about  three  miles,  and  delivered  to  some  of  the  wheels  with  a  head  of 
627  feet.  The  other  wheels  at  this  plant  receive  water  drawn  from  the 
same  creek  by  a  pipe  line  about  six  miles  long.  A  large  part  of  this  line 
is  composed  of  31 -inch  cement  pipe,  laid  in  trenches  and  tunnels.  The 
water  in  the  8,000  feet  of  pipe  next  to  the  power-house  has  a  fall  of  1,960 
feet,  and  this  pipe  is  of  steel  and  24  and  26  inches  in  diameter.  The 
head  of  1,960  feet,  minus  friction  losses  in  the  steel  pipes,  is  delivered  at 
the  wheels. 

From  the  foregoing  it  appears  that  in  a  space  of  eight  miles  along 
Mill  Creek  there  is  a  fall  of  more  than  2,490  feet.  To  utilize  this  fall, 
water  is  diverted  from  the  creek  at  three  points  within  a  distance  of  six 
miles  and  delivered  in  two  power-stations  under  three  different  heads. 
As  the  stream  gathers  in  volume  between  the  upper  and  the  lower  in- 
takes, an  equal  amount  of  power  could  have  been  developed  in  a  single 
station  only  by  taking  the  three  separate  conduits  or  pipe  lines  to  it  and 
delivering  their  water  there  at  three  heads. 

Whether  the  expense  of  extending  conduits  and  pipe  lines  to  a  single 
generating  station  will  more  than  offset  the  advantages  to  be  gained 
thereby  is  a  question  that  should  be  decided  on  a  number  of  factors  vary- 
ing with  each  case.  In  general,  it  may  be  said  that  the  smaller  the 
volume  of  water  to  be  handled  and  the  greater  its  head,  the  more  ad- 
vantageous is  it  to  concentrate  the  generating  machinery  in  the  smallest 
practicable  number  of  stations. 

On  the  Santa  Ana  River,  into  which  Mill  Creek  flows,  the  Santa 
Ana  plant,  whence  energy  is  transmitted  to  Los  Angeles,  is  located. 
Water  reaches  this  plant  through  a  conduit  of  tunnels,  flumes,  and  pipes, 
with  a  total  length  of  about  three  miles  from  the  point  where  the  flow  of 
the  river  is  diverted.  The  2,210  feet  of  this  conduit  nearest  the  power- 
plant  are  composed  of  30-inch  steel  pipe,  with  a  fall  of  728  feet. 

Within  fifteen  miles  of  Mexico  City  are  five  water-power  stations  that 
supply  energy  for  its  electrical  system.  Two  of  these  stations  are  on  the 


LOCATION  OF  WATER-POWER  STATIONS. 


77 


Monte  Alto  and  three  are  on  the  Tlaluepantla  River,  the  two  former 
stations  being  about  three  miles,  and  the  more  distant  of  the  three  latter 
stations  five  miles,  apart.  At  a  distance  of  several  miles  above  the  highest 
station  on  each  river  the  water  is  diverted  by  a  canal,  and  the  water  of 
each  of  these  canals,  after  passing  through  the  wheels  of  the  highest 
station,  goes  on  to  the  remaining  station,  or  stations,  on  the  same  river 
by  a  continuation  of  the  canal. 

By  placing  the  stations  so  short  a  distance  apart  the  head  of  water 
at  each  station  is  reduced.     On  one  stream  these  heads  are  492  and  594 


FIG.  20.— Wood  Pipe  Line  to  Pike's  Peak  Power-house. 

feet  respectively,  and  at  two  of  the  stations  on  the  other  stream  they  are 
547  and  295  feet  respectively.  This  division  of  the  total  head  of  water 
afforded  by  each  river  results  in  a  rather  small  capacity  for  each  station, 
the  total  at  the  five  plants  being  only  4,225  kilowatts. 

In  contrast  with  this  figure  the  already  mentioned  Electra  plant  has 
generators  of  10,000,  the  Santa  Ana  plant  generators  of  3,000,  and  the 
larger  of  the  two  Mill  Creek  plants  generators  of  3,500  kilowatts  capac- 
ity. It  should  be  noted  that  the  cost  of  operation,  as  well  as  that  of 
original  construction,  will  vary  materially  between  one  large  and  several 
smaller  stations  of  equal  total  capacity,  the  advantage  as  to  operative  cost 
being  obviously  with  the  one  large  plant. 


78      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


O 
O 
CQ 


Crib  Dam,  Rock  Filled 


LOCATION  OF  WATER-POWER  STATIONS.  79 

All  of  the  power-stations  here  considered  have  been  equipped  with 
water-wheels  and  generators  operating  on  horizontal  shafts,  and  this  is 
the  general  practice.  This  arrangement  brings  the  generators  and  the 
floor  of  the  power-station  within  a  few  feet  of  the  level  of  the  tail-water. 
By  the  general  use  of  draught  tubes  with  turbine  wheels  the  floors  of  sta- 
tions are  often  kept  twenty  feet  or  more  above  the  tail-water  level. 

Where  the  total  available  head  of  water  is  quite  small,  as  is  often  the 
case  with  rivers  where  the  volume  of  water  is  great,  it  is  generally  neces- 
sary to  bring  the  level  of  the  station  floor  down  to  within  a  few  feet  of 
the  tail-water.  The  Birchem  Bend  station  of  the  Springfield,  Mass., 
electric  system  affords  a  good  example  of  this  sort,  the  floor  of  this  station 
being  only  2.6  feet  above  the  ordinary  level  of  the  tail- water.  At  this 
station  the  difference  of  level  between  the  head-  and  tail-water  is  only 
fourteen  feet,  and  even  with  the  low  floor  level  named  the  top  sides  of  the 
horizontal  turbine  wheels  are  covered  only  by  4.5  feet  of  water. 

At  the  Garvin's  Falls  station  of  the  Manchester,  N.  H.,  electric  sys- 
tem the  level  of  the  floor  of  the  generator  room  is  thirteen  feet  above 
the  ordinary  level  of  the  Merrimac  River,  on  the  bank  of  which  this  sta- 
tion is  located ;  but  in  this  case  the  total  head  of  water  is  about  twenty- 
eight  feet.  The  high  water  of  the  Merrimac  in  1896,  before  the  Garvin's 
Falls  station  was  built,  reached  a  point  5.24  feet  above  its  present  floor 
level,  and  18.24  feet  above  the  ordinary  level  of  the  river  at  the  point 
where  the  station  is  located. 

Under  the  Red  Bridge  electric  station  of  the  Ludlow  Manufacturing 
Company,  on  the  Chicopee  River,  in  Massachusetts,  the  tail-water  is 
twenty  feet  below  the  level  of  the  floor  and  twenty- four  feet  below  the  cen- 
tres of  the  water-wheel  and  generator  shafts.  The  difference  between 
wheel-shaft  and  tail- water  levels  at  this  station  is  near  the  maximum  that 
can  be  attained  with  horizontal  pressure  turbines,  because  a  draught 
tube  much  longer  than  twenty-five  feet  does  not  give  good  results. 

In  a  pressure  turbine  the  guides  and  wheel  must  be  completely  filled 
with  water,  as  must  also  the  draught  tube,  for  efficient  operation.  If 
draught  tubes  are  much  more  than  twenty-five  feet  long,  it  is  hard  to  keep 
a  solid  column  of  water  from  turbine  to  tail-water  in  each,  and  if  this  is  not 
done  a  part  of  the  head  of  water  becomes  ineffective.  As  pressure  tur- 
bines are  employed  almost  exclusively  at  electric  stations  with  low  heads 
of  water,  it  is  frequently  impossible  to  locate  such  stations  above  tlie  pos- 
sible level  of  tail-water  in  times  of  flood  if  horizontal  wheels  direct-con- 
nected to  generators  are  employed. 

If  turbines  with  vertical  shafts  are  to  be  used,  a  power-station  may  be 


8o       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


LOCATION  OF  WATER-POWER  STATIONS. 


81 


so  located  or  constructed  that  all  the  electrical  equipment  will  be  above 
the  highest  known  water-mark.  With  vertical  shafts,  connecting  wheels, 
and  generators,  the  main  floor  of  an  electric  station  may  be  located  above 
the  crest  of  the  falls  where  the  power  is  developed  instead  of  at  or  near 
their  base. 

By  far  the  most  important  examples  of  electric  stations  laid  out  on  this 
plan  are  those  at  Niagara  Falls,  where  there  are  four  such  plants.     Two 


FIG.  23.— Power-house  No.  2  at  Niagara  Falls. 

of  these  generating  plants,  with  an  aggregate  capacity  of  105,000  horse- 
power, stand  a  mile  above  the  falls,  and  are  supplied  with  water  through 
a  short  canal  from  Niagara  River.  Beneath  each  of  these  two  stations  a 
long,  narrow  wheel  pit  has  been  excavated  through  rock  to  a  depth  of  172 
feet  below  the  level  of  water  in  the  canal.  Both  wheel  pits  terminate  in 
a  tunnel  7,000  feet  long  that  opens  into  the  river  below  the  falls. 

In  this  wheel  pit  the  tail-water  level  is  161  feet  below  that  of  the  water 
in  the  canal,  and  166  feet  below  the  floor  of  the  power-station.  Water 
passes  from  the  canal  down  the  wheel  pits  to  the  wheels  near  the  bottom 
through  steel  penstocks,  each  seven  feet  in  diameter,  and  a  vertical  shaft 
extends  from  each  wheel  case  to  a  generator  in  the  station  above. 

Locations  like  that  at  Niagara  give  great  security  against  high  water 
and  washouts,  but  are  seldom  adopted  because  of  the  large  first  cost  of 
plant  construction.  With  heads  of  water  from  several  hundred  to  2,000 
feet  the  loss  of  a  few  feet  of  head  reduces  the  available  power 'to  only  a 


82       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


very  slight  extent,  and  impulse  wheels  are  usually  employed.  Draught 
tubes  are  not  available  to  increase  the  heads  at  such  wheels,  and  any 
fall  of  the  water  after  it  leaves  the  wheels  does  no  useful  work. 


Electric  stations  driven  by  impulse  wheels  under  great  heads,  like 
those  at  Colgate,  Electra,  Kern  River,  Santa  Ana  River,  and  Mill  Creek, 
may  be  located  far  enough  above  the  beds  of  their  water-courses  to  avoid 
dangers  from  freshets,  without  serious  loss  of  available  power. 


CHAPTER  VIII. 


DESIGN  OF  ELECTRIC  WATER-POWER  STATIONS. 

WATER- WHEELS  must  be  located  at  some  elevation  between  that  of 
head-  and  tail-water.  With  horizontal  shafts  and  direct-connected  wheels 
and  generators  the  main  floor  of  the  station  is  brought  below  the  level  of 
the  wheel  centres.  This  is  much  the  most  general  type  of  construction, 
and  was  followed  in  the  Massena,  Sault  Ste.  Marie,  Canon  Ferry,  Col- 


FlG.  25.— Cross  Section  of  Columbus,  Ga.,  Power-station. 

gate,  Electra,  Santa  Ana,  and  many  other  well-known  water-power  sta- 
tions. If  horizontal  shafts  are  employed  for  wheels  and  generators  with 
belt  or  rope  connections  between  them  the  floor  of  the  generator  room 
may  be  elevated  a  number  of  feet  above  the  wheels.  This  difference  of 
elevation  is  usually  provided  for  either  by  upper  and  lower  parts  of  the 
same  room,  or  by  separate  rooms  one  above  the  other  and  a  floor  between 
them.  A  two-story  construction  of  this  latter  sort  was  frequently  adopted 

83 


84      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

in  the  older  water-power  stations,  and  good  examples  of  it  may  be  seen  in 
connection  with  the  electrical  supply  system  at  Burlington,  Vt.,  and  the 
Indian  Orchard  station  in  the  Springfield,  Mass.,  system.  Vertical 
wheel  shafts  make  the  elevation  of  the  main  or  generator  floor  of  a  station 
independent  of  that  of  the  wheels,  and  thus  give  the  highest  degree  of 
security  against  high  water.  After  the  vertical  wheel  shaft  reaches  the 
generator  room,  it  may  be  geared  to  a  horizontal  shaft  that  has  one  or 
more  dynamos  directly  mounted  on  it,  or  drives  dynamos  through  belts 
or  ropes.  Belt-driving  in  this  way,  from  horizontal  shafts  connected  by 
bevel  gears  with  vertical  wheel  shafts,  is  not  uncommon  in  the  older  class 
of  water-power  stations.  Generators  mounted  singly  or  in  pairs  on  hori- 


FiG.  26.— Cross  Section  of  Combined  Steam-  and  Water-power  Station  at  Richmond,  Va. 

zontal  shafts  that  are  driven  by  gearing  on  vertical  wheel  shafts  have 
been  adopted  at  the  Lachine  Rapids  and  South  Bend  plants,  and  it 
seems  to  offer  a  desirable  method  of  connection  in  cases  where  vertical 
wheels  are  necessary  and  the  cost  of  generators  must  be  kept  at  a  low 
figure.  With  this  method  of  driving  the  generators  can  be  designed  for 
any  economical  speed  and  step  bearings  avoided. 

The  most  desirable  method  of  driving  generators  with  vertical  wheels, 
where  the  expense,  is  not  too  great,  is  the  direct  mounting  of  each  gen- 


DESIGN  OF  WATER-POWER  STATIONS.  85 

erator  on  the  upper  end  of  a  wheel  shaft  (see  cut).  This  method  of  con- 
nection not  only  requires  a  special  type  of  generator,  but  may  put  serious 
limits  on  its  speed.  In  general,  the  peripheral  speed  of  a  pressure  turbine 
should  be  about  75  per  cent  of  the  theoretical  velocity  of  water  issuing 
under  a  head  equal  to  that  at  which  the  wheel  operates,  in  order  to  give 
the  best  efficiency.  The  rotative  speeds  of  turbines,  operating  under  any 
given  head,  should  thus  increase  as  their  capacities  and  diameters  de- 
crease. Because  of  these  principles  it  is  the  common  practice,  with  hori- 
zontal wheels,  to  mount  two  or  more  on  each  shaft  to  which  a  generator 


FIG.  27.— Cross  Section  of  Wheel  House  at  Buchanan,  Mich. 

is  direct-connected  in  order  to  obtain  a  greater  speed  of  rotation  than 
could  be  obtained  with  a  single  wheel  of  their  combined  power.  Thus, 
at  Sault  Ste.  Marie  the  horizontal  shaft  on  which  each  4oo-kilowatt  gen- 
erator is  mounted  is  driven  at  180  revolutions  per  minute  by  four  turbines 
under  a  head  of  about  20  feet.  At  Massena  the  head  of  water  is  50  feet, 
and  each  5,000  horse-power  generator  is  driven  at  150  revolutions  per  min- 
ute by  six  turbines  on  a  horizontal  shaft.  Vertical  turbines  are  sometimes 
mounted  singly  on  their  shafts,  as  was  done  in  the  hydroelectric  plant  at 
Oregon  City  on  the  Willamette  River,  and  this  practice  gives  speeds  that 


86      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

are  too  low  for  direct-connected  dynamos  of  moderate  cost,  unless  the 
head  of  water  is  unusually  great.  At  the  Oregon  City  plant  the  head  of 
water  is  only  40  feet,  and  yet  a  single  42-inch  turbine  was  mounted  on  the 
vertical  shaft  that  drives  each  generator. 

The  most  notable  examples  of  direct-connected  generators  and  ver- 
tical turbines  is  that  at  Niagara  Falls,  where  twenty-one  generators  of 
5,000  horse-power  each  are  mounted  at  the  tops  of  as  many  vertical 
wheel  shafts  in  two  of  the  four  stations.  Each  vertical  shaft  in  the 
Niagara  stations  is  driven  at  250  revolutions  per  minute  by  a  pair  of 


Generator  Room 


FIG.  28.— Longitudinal  Section  of  Buchanan,  Mich.,  Power-house. 

turbines,  one  above  the  other.  The  maximum  head  between  the  water 
in  the  Niagara  canal  and  that  in  the  tunnel  which  forms  the  tail-race 
is  161  feet.  On  ten  shafts  the  centres  of  the  wheel  cases  are  136  feet 
below  the  level  of  water  in  the  canal,  and  no  draft  tubes  are  used. 

The  eleven  pairs  of  wheels  at  the  second  Niagara  power-house  have 
their  centre  line  128.25  feet  below  the  canal  level  and  a  draft  tube  for  each 
pair  of  wheels  extends  to  a  point  below  the 'tail-water  level.  It  is 
entirely  practicable  to  use  more  than  a  single  pair  of  turbines  on  the 
same  vertical  shaft,  as  is  shown  at  the  Hagneck  station  on  the  Jura,  in 


DESIGN  OF  WATER-POWER  STATIONS. 


FIG.  29. — Section  of  Power-house  No.  2  at  Niatrara  Falls 


88      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


DESIGN  OF  WATER-POWER  STATIONS.      .        89 

Switzerland,  where  the  head  of  water  is  about  twenty-one  feet  and  four 
turbines  are  mounted  on  each  vertical  shaft.  The  combined  capacity 
of  these  four  wheels  on  each  shaft  is  1,500  horse-power  and  its  speed 
is  100  revolutions  per  minute.  At  the  top  of  each  shaft  an  8,000- volt 
generator,  with  external,  revolving  magnet  frame,  is  mounted.  The 
use  of  four  wheels  per  vertical  shaft  presents  no  great  difficulty  and 
should  be  resorted  to  more  frequently  in  the  future. 

For  horizontal,  direct-connected  turbine  wheels  and  generators  the 
nearly  uniform  practice  is  to  locate  the  generators  in  a  single  row  from 
one  end  of  a  station  to  the  other,  and  this  brings  the  turbines  into  a  paral- 
lel row.  On  this  plan  the  shaft  of  each  connected  generator  and  its 
group  of  turbines  sets  at  right  angles  to  the  longer  sides  of  a  station  and 
approximately  parallel  with  the  direction  in  which  water  flows  to  the 
wheels.  The  typical  water-power  station  with  direct-connected  units  is 
thus  a  rather  long,  narrow  building  into  which  water  enters  on  one  side 
through  penstocks  and  leaves  on  the  other  through  tail-races.  Such  sta- 
tions usually  set  with  one  of  the  longer  sides  parallel  to  the  river  into 
which  the  tail-water  passes  and  between  this  river  and  the  canal  or  pipe 
line.  At  Massena  the  electric  station  occupies  the  position  of  a  dam  be- 
tween the  end  of  the  power  canal  and  the  Grass  River,  being  about  150 
feet  wide  and  550  feet  long.  Canal  water  entering  this  station  passes 
through  its  wheels  to  the  river  under  a  head  of  about  50  feet.  A  similar 
construction  was  followed  at  Sault  Ste.  Marie,  where  the  power-station 
separates  the  end  of  the  canal  from  the  St.  Mary's  River.  This  station  is 
100  feet  wide,  1,368  feet  long,  and  is  to  contain  80  sets  of  horizontal 
wheels,  each  set  being  connected  to  its  own  generator,  and  through  these 
wheels  the  canal  water  passes  under  a  head  of  approximately  20  feet.  Ten 
generators  are  placed  in  line  at  the  Canon  Ferry  station  which  is  225  by  50 
feet  inside,  and  each  generator  is  driven  by  a  pair  of  horizontal  wheels 
under  a  head  of  30  feet.  This  station  sets  between  a  short  canal  and  the 
Missouri  River,  near  one  end  of  the  dam.  Passing  from  water-heads  of 
less  than  50  to  those  of  several  hundred  or  even  more  than  i  ,000  feet,  the 
general  type  of  station  building  remains  about  the  same,  but  there  is  an 
important  change  in  the  arrangement  of  direct-connected  wheels  and 
generators.  With  these  high  heads  of  water,  wheels  of  the  impulse  type, 
to  which  the  water  is  supplied  in  the  form  of  jets  from  nozzles,  are  em- 
ployed. These  jets  pass  to  the  wheels  in  planes  at  right  angles  to  their 
shafts,  instead  of  flowing  in  lines  parallel  to  these  shafts  like  water  to  pres- 
sure turbines.  The  shafts  of  impulse  wheels  and  their  direct-connected 
generators  are  consequently  arranged  parallel  with  the  longer  instead  of 


9o      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  shorter  sides  of  their  stations.  This  plan  results  in  long,  narrow  sta- 
tions with  water  entering  at  one  and  leaving  at  the  other  of  the  longer 
sides,  just  as  in  the  case  of  direct-connected  turbines  under  moderate 
heads.  Stations  with  direct-connected  impulse  wheels  are  even  longer 


-45  ft 


30'x80' 
FIG.  31.— Plan  of  Generating  Station  near  Cedar  Lake  for  City  of  Seattle,  Wash. 

for  a  given  number  and  capacity  of  units  than  are  stations  with  pres- 
sure turbines.  Colgate  power-house,  on  the  North  Yuba  River,  contains 
seven  generators,  each  direct-connected  to  an  impulse  wheel  and  shafts 
all  parallel  to  its  longer  sides.  This  station  is  275  feet  long  by  40  feet 
wide,  and  the  water  which  enters  one  side  by  five  iron  pipes,  30  inches 


DESIGN  OF  WATER-POWER  STATIONS. 


92      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

each  in  diameter,  under  a  head  of  about  700  feet,  is  discharged  from  the 
other  side  into  the  river. 

At  Electra  station  on  the  Mokelumne  River  five  pairs  of  impulse 
wheels  are  direct-connected  to  five  generators,  each  unit  having  its  shaft 


k- 


Flu.  33. —  Plan  of  Power-station  at  Great  Falls. 


diagonal  with  the  walls  of  the  building,  and  pipes  deliver  water  to  the 
wheels  under  a  head  of  1,450  feet.  The  ground  plan  of  the  generator 
room  at  this  plant  is  40  by  208  feet.  The  power-station  on  Santa  Ana 
River,  whence  energy  is  transmitted  83  miles  to  Los  Angeles,  measures 
127  feet  long  and  36  feet  wide  inside,  and  contains  four  generating  units 


DESIGN  OF  WATER-POWER  STATIONS.  93 

in  line,  each  of  which  consists  of  a  direct-connected  dynamo  and  impulse 
wheel,  with  shafts  parallel  to  the  longer  sides  of  the  station.  Jets  driving 
the  wheels  in  this  station  are  delivered  under  a  head  of  728  feet  minus 
the  loss  by  friction  in  a  penstock  2,210  feet  long. 

Both  of  the  first  Niagara  plants,  with  vertical  wheels  far  below  the  sta- 
tions in  the  pits,  are  long  and  narrow  and  have  their  generators  in  a  single 
row.  The  later  of  these  two  stations  has  a  ground  area  of  approximately 
72  by  496  feet  outside,  and  contains  eleven  generators  all  in  line.  From 
these  examples  it  may  be  seen  that  the  prevailing  type  of  electric  water- 
power  station,  whether  designed  for  horizontal  or  vertical  wheels  of  either 
the  pressure  or  impulse  type,  is  wide  enough  for  only  a  single  row  of  gen- 


r 


FIG,  34.— Power-house  at  Red  Bridge  on  Chicopee  River. 

erators  and  wheels,  and  has  sufficient  length  to  accommodate  the  required 
number  of  units. 

A  few  modern  stations  that  depart  from  this  general  plan  will  be 
found,  as  that  at  Great  Falls,  on  the  Presumpscot  River,  whence  elec- 
trical supply  for  Portland,  Me.,  is  drawn.  This  station  sets  about  forty 
feet  in  front  of  the  forebay  end  of  the  dam,  and  two  penstocks  enter  the 
rear  wall,  while  the  other  two  enter  one  each  through  two  of  the  remaining 
opposite  sides.  Of  the  four  generators,  with  their  direct-connected 


94       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


wheels,  two  are  arranged  with  parallel  shafts,  while  the  other  two  have 
their  shafts  in  line  and  at  right  angles  to  the  lines  of  the  former  two. 
The  station  containing  these  generating  sets  has  a  floor  area  of  55  by 
67.5  feet. 

Modern  electric  stations  driven  by  water-po\ver  are  usually  but  one 
story  in  height  and  are  clear  inside  from  floor  to  roof,  save  for  cranes  and 
roof  trusses.  This  construction  may  be  seen  in  the  Niagara,  Spier  Falls, 


lilHijjijg  5tms        [£-T:KI 

J!|||      !j      T*2-!2^  tl-2**^ 


^^rs 

i  ^^i^took : 


FIG.  35.— Plan  and  Elevation  of  Red  Bridge  Station  on  the  Chicopee  River. 

Canon  Ferry,  Colgate,  Electra,  Santa  Ana  River  and  many  other  notable 
plants.  In  spite  of  this  one-story  style  of  construction,  the  electric  sta- 
tions reach  fair  elevations  because  of  the  necessity  for  head  room  to  oper- 
ate cranes  in  placing  and  removing  generators.  At  Garvin's  Falls,  on 
the  Merrimac  River,  the  electric  station  contains  generators  of  650  kilo- 
watts each  and  the  distance  from  floor  to  the  lower  cords  of  roof  trusses 
is  27  feet.  In  the  station  at  Red  Bridge,  on  the  Chicopee  River,  where 
generators  are  of  i  ,000  kilowatts  capacity  each,  the  distance  between  floor 


DESIGN  OF  WATER-POWER  STATIONS.  95 

and  the  under  side  of  roof  beams  is  30.66  feet.  Between  the  floor  and 
roof  trusses  at  the  Birchem  Bend  station,  on  the  river  last  named,  the  dis- 
tance is  26.25  feet,  but  each  generator  is  rated  at  only  400  kilowatts.  In 
the  Canon  Ferry  plant,  with  its  generators  of  750  kilowatts  each,  the  dis- 
tance from  floor  to  roof  trusses  is  28  feet.  At  the  plant  on  Santa  Ana 
River,  the  750-kilowatt  generators,  being  connected  to  impulse- wheels, 
operate  at  300  revolutions  per  minute,  have  relatively  small  diameters  and 
are  mounted  over  pits  in  the  floor  so  that  their  shaft  centres  are  only 
about  two  feet  above  it.  By  these  means  the  distance  from  floor  to  roof 
trusses  was  reduced  to  18.25  feet.  All  these  examples  of  elevations  be- 
tween floors  and  roof  supports  are  for  stations  with  direct-connected  gen- 
erators and  horizontal  wheels.  In  the  new  Niagara  station,  where  gen- 
erators of  3,750  kilowatts  each  are  mounted  oh'  vertical  wheel  shafts  that 
rise  from  the  floor,  the  distance  between  the  floor  and  roof  trusses  is 
39.5  feet. 

Electric  stations  driven  by  water-power  are  now  constructed  almost 
entirely  of  materials  that  will  not  burn — that  is,  stone,  brick,  tile,  concrete, 
cement,  iron,  and  steel.  Stone  masonry  laid  with  cement  mortar  cr  con- 
crete masonry  is  very  generally  employed  for  all  those  parts  of  the  foun- 
dations that  come  in  contact  with  the  tail-water.  For  sub-foundations 
bedrock  is  very  desirable,  but  where  this  cannot  be  reached  piles  are  driven 
closely  and  their  tops  covered  with  several  feet  of  cement  concrete  as  a 
bedding  for  the  stone  foundation.  Where  stone  is  plenty  or  bricks  hard 
to  obtain,  the  entire  walls  of  a  water-power  station  are  frequently  laid  en- 
tirely with  stone  in  concrete  mortar.  If  bricks  can  readily  be  had  they  are 
more  commonly  used  than  stone  for  station  walls  above  the  foundations. 
Concrete  formed  into  a  monolithic  mass  is  a  favorite  type  of  construction 
for  the  foundations,  walls  and  floors  of  water-power  plants  in  Southern 
California.  Cement  and  concrete  are  much  used  for  station  floors  in  all 
parts  of  the  country,  and  these  floors  are  supported  by  masonry  arches 
in  cases  where  the  tail-water  flows  underneath  the  station  after  leaving 
the  wheels.  Station  roofs  are  usually  supported  by  steel  trusses  or  I- 
beams,  and  slate  and  iron  are  favorite  roof  materials.  With  iron  roof- 
plates  an  interior  lining  of  wood,  asbestos,  or  some  other  poor  conductor 
of  heat  is  much  used  to  prevent  the  condensation  of  water  on  the  under 
side  of  the  roof  in  cold  weather.  Walls  of  water-power  stations  are 
usually  given  sufficient  thickness  of  masonry  to  support  all  loads  that 
come  upon  them  without  the  aid  of  steel  columns.  In  some  cases 
where  cranes  do  not  extend  entirely  across  their  stations,  one  end  of 
each  crane  is  supported  by  one  of  the  station  walls  and  the  other  end 


96      ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

by  a  row  of  iron  or  steel  columns  rising  from  the  floor.  Where  the 
generator-room  of  a  station  has  its  floor  level  below  high-water  mark 
especial  care  should  be  taken  to  make  the  walls  water-proof  to  an  ele- 
vation above  this  mark.  As  the  travelling-crane  and  the  loads  which 
it  carries  in  erecting  wheels  and  generators  form  a  large  part  of  the 
weight  on  the  station  walls,  these  walls  are  often  reduced  as  much  as 
one-half  in  thickness  at  the  level  of  the  crane,  thus  forming  benches 
on  which  the  ends  of  the  cranes  rest. 

The  Garvin's  Falls  station,  on  the  Merrimac  River,  rests  on  arches 
of  stone  masonry  through  which  the  tail-water  passes,  and  the  brick  walls 


FIG.  36. — Steel  Penstocks  at  Chamblay  Power-house. 

are  water-proofed  to  an  elevation  eight  feet  above  the  floor.  At  twenty 
feet  above  the  floor  the  twenty-four-inch  brick  walls  on  the  two  longer 
sides  are  reduced  to  eight  inches  in  thickness,  thus  forming  benches  each 
sixteen  inches  wide  on  which  the  crane  travels.  Arches  of  stone  masonry 
support  the  twenty-four-inch  brick  walls  of  the  station  at  Red  Bridge,  on 
the  Chicopee  River,  and  these  walls  on  the  two  longer  sides  decrease  in 
thickness  to  twelve  inches  at  an  elevation  of  twenty-one  feet  above  the 
floor,  thus  forming  benches  twelve  inches  wide  for  the  ends  of  the  crane. 
One  concrete  wall  of  the  Santa  Ana  station  is  2.5  feet  thick  to  a  dis- 


DESIGN  OF  WATER-POWER  STATIONS.  97 

tance  of  13.5  feet  above  the  floor,  and  th<m  shrinks  to  a  thickness  of  1.5 
feet,  corresponding  to  that  of  the  opposite  wall,  thus  forming  a  bench 
twelve  inches  wide  for  one  end  of  the  crane.  The  other  end  of  the  crane 
in  this  case  is  supported  by  an  I-beam  on  a  row  of  iron  columns. 

It  is  not  uncommon  to  locate  horizontal  turbines  in  a  room  separate 
from  that  occupied  by  the  generators  to  which  they  are  direct-connected, 
in  order  to  protect  the  latter  from  water  in  the  event  of  a  break  in  pen- 
stocks or  wheel  cases.  In  cases  of  this  sort  the  shafts  connecting  wheels 
and  generators  pass  through  the  wall  between  them.  The  horizontal 
turbines  may  be  located  at  the  bottom  of  a  canal  whose  water  presses 
against  the  wall  through  which  the  wheel  shafts  pass,  or  they  may  be 
contained  in  iron  cases  at  the  ends  of  penstocks.  In  this  latter  case  an 
extension  of  the  station  is  often  provided  for  a  wheel  room  to  contain 
these  cases.  Such  wheel  rooms  are  long,  narrow,  low-roofed  and  parallel 
to  the  generator  rooms  of  their  stations.  The  floors  of  these  wheel  rooms 
are  at  nearly  the  same  levels  as  the  floors  of  generator  rooms,  but  eleva- 
tions of  their  roofs  above  the  floors  are  much  less  than  like  elevations  in 
the  main  parts  of  the  stations.  The  Garvin's  Falls,  Red  Bridge,  and 
Apple  River  stations  have  wheel  rooms  of  the  type  just  described.  With 
impulse-wheels  to  which  water  passes  in  planes  at  right  angles  to  their 
shafts  it  is  desirable,  in  order  to  avoid  changes  in  the  direction  of  water 
pipes,  that  direct-connected  wheels  and  generators  occupy  the  same  room, 
and  this  is  the  arrangement  at  the  Colgate,  Electra,  Santa  Ana,  Mill 
Creek,  and  many  other  power-houses  using  such  equipments.  The  area 
of  a  wheel  room  may  frequently  be  reduced  at  stations  operating  direct- 
connected  horizontal-pressure  turbines  under  low  heads  by  placing  the 
wheels  at  the  bottom  of  the  canal  which  has  one  side  of  the  station  or  gen- 
erator room  for  a  retaining  wall.  This  plan  was  adopted  at  the  Birchem 
Bend  plant  with  a  head  of  fourteen  feet,  and  at  the  Sault  Ste.  Marie 
station  where  the  head  of  water  is  about  twenty  feet.  Vertical  wheels 
direct-connected  to  generators  must  be  directly  underneath  the  main 
room  of  their  station,  and  may  be  in  a  canal  over  which  the  station  is 
built,  in  a  wheel  room  that  forms  its  lower  part,  or  in  a  wheel  pit  and 
supplied  with  water  through  penstocks,  as  at  the  Niagara  Falls  plants. 

Step-up  transformers  developing  very  high  voltages  are  not  an  ele- 
ment of  safety  in  a  generator  room,  and  the  better  practice  is  to  locate 
them  in  a  separate  apartment  by  themselves,  if  not  in  a  separate  building. 
For  the  Niagara  Falls  plant,  the  transformers  that  deliver  three-phase 
current  at  22,000  volts  are  located  in  a  building  across  the  canal  from  the 
generating  plant.  At  Canon  Ferry  the  transformers  operating  at  50,000 


98       ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

volts,  three-phase,  are  located  in  a  steel  and  iron  addition  to  the  power- 
house. Transformers  at  Electra  station,  which  are  intended  to  work 
ultimately  at  60,000  volts,  are  located  in  an  extension  of  the  main  build- 
ing and  are  separated  from  the  generator-room  by  a  wall.  At  the  Santa 
Ana  plant  the  33,000- volt  transformers  are  grouped  in  one  corner  of  the 
generator  room,  but  no  partition  separates  their  space  from  the  remainder 
of  the  room.  In  the  Colgate  plant  the  transformers,  working  at  40,000 
volts,  are  spaced  along  one  of  the  longer  sides  of  the  station  opposite  to 
and  only  a  few  feet  from  the  row  of  generators.  One  end  of  the  main 
room  in  the  Apple  River  plant  is  devoted  exclusively  to  the  2 5,000- volt 


FIG.  37.— One  of  the  Turbine  Wheels  at  Spier  Falls  on  the  Hudson  River. 

transformers,  and  there  is  a  distance  of  about  twenty-seven  feet  between 
them  and  the  nearest  generator.  The  highest  degree  of  safety  for  trans- 
formers at  these  great  voltages  seems  to  require  that  they  be  located  in  a 
separate  room  where  the  floor,  walls,  and  roof  are  made  entirely  of  in- 
combustible material. 

Water  supplied  to  horizontal  turbine  wheels  under  moderate  heads 
usually  enters  the  station  by  penstocks  on  one  side  and  leaves  it  by  the 
tail-race  on  the  other,  but  this  is  not  true  in  every  case.  At  the  Birchem 
Bend  plant,  the  canal  in  which  the  wheels  are  located  being  between  the 


DESIGN  OF  WATER-POWER  STATIONS.  99 

station  and  the  river,  water  never  enters  or  passes  under  the  station, 
which  has  a  continuous  foundation.  So  again  at  the  Apple  River  plant 
the  single  supply  pipe,  twelve  feet  in  diameter  and  delivering  water  under 
a  head  of  eighty-two  feet,  lies  parallel  with  the  greater  length  of  the  sta- 
tion and  between  it  and  the  river.  Short  penstocks  pass  from  this  supply 
pipe  into  the  wheel  section  of  the  power-house,  and  the  water  after  pass- 
ing through  the  wheels  flows  out  to  the  river  between  the  masonry  piers 
that  support  the  twelve-foot  pipe.  The  generator  section  of  this  station 
has  thus  no  water  flowing  under  it.  An  interesting  distinction  may  be 
noted  between  the  conditions  as  to  the  tail-water  about  the  foundations  of 
stations  working  under  low  and  those  under  great  water  heads.  In  cases 
of  the  former  sort  the  volumes  of  water  are  relatively  great  and  the  foun- 
dations of  stations  are  usually  submerged,  and  much  reduced  in  area  to 
make  room  for  the  tail-races.  Thus,  the  foundations  of  the  station  at 
Red  Bridge,  where  there  is  49  feet  head,  have  nearly  all  of  their  footings 
under  water,  and  of  a  total  length  of  145  feet  at  the  top  of  these  founda- 
tions the  six  tail-races  underneath  cut  out  92  feet.  These  tail-races  ex- 
tend underneath  both  the  wheel  and  generator  rooms. 

Where  power  is  derived  from  water  delivered  under  great  head  from 
pipe  nozzles  to  impulse-wheels,  stations  are  usually  well  above  the  water 
levels  of  streams  into  which  they  discharge,  and  passages  for  tail-water 
underneath  the  station  shrink  to  small  tunnels  through  their  foundations. 
Seven  of  these  tunnels  have  a  total  width  of  less  than  25  feet  at  the  Santa 
Ana  River  station,  which  is  127  feet  long,  and  where  the  head  of  water 
is  728  feet.  At  the  Colgate  plant,  with  its  head  of  700  feet,  the  water, 
at  times  of  light  load,  instead  of  flowing  out  of  its  passages  underneath 
the  station,  shoots  from  the  pipe  nozzles  clear  across  the  North  Yuba 
River  on  the  bank  of  which  the  station  stands. 

In  a  comparison  of  floor  areas  per  kilowatt  of  main  generator  capac- 
ities in  electric  stations  using  water-  and  those  using  steam-power,  the 
matter  of  space  for  transformers  may  be  entirely  omitted,  because  the 
extent  of  this  space  is  independent  of  the  type  or  location  of  water-wheels, 
or  the  difference  of  water  and  steam  as  motive  powers.  Where  water- 
wheels  and  their  connected  generators  occupy  separate  rooms,  as  is  often 
the  case  with  turbines  under  low  pressures,  the  wheel  room  has  a  little 
less  length,  and  is  generally  narrower  than  the  generator  room.  Thus, 
at  the  Red  Bridge  station  the  generator  room  is  141  feet  long  and  the 
wheel  room  about  127  feet,  while  the  former  is  33.33  feet  and  the  latter 
24  feet  wide.  So  again  at  Apple  River  Falls  the  generator  room  is  140 
by  30  feet  and  the  wheel  room  1 06  by  22  feet,  the  generator  room  in  this 


joo    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


DESIGN  OF  WATER-POWER  STATIONS.  101 

case  containing  also  transformers.  It  follows  that  if  wheels  can  be  lo- 
cated outside  of  the  station,  as  in  a  canal,  quite  a  reduction  in  its  total  floor 
area  can  be  made,  which  may  easily  range  from  20  to  40  per  cent.  The 
kilowatt  capacity  per  square  foot  of  floor  area  in  both  wheel  and  genera- 
tor rooms  combined  tends  to  increase  with  the  individual  capacity  of  the 
generating  units.  Generators  on  vertical  shafts  seem  to  require  about 
as  much  floor  space  per  unit  of  capacity  as  do  generators  on  horizontal 
shafts.  In  the  Red  Bridge  station  the  total  capacity  is  4,800  kilowatts 
of  main  generators  in  six  horizontal  units,  and  the  area  of  the  generator 
room  alone  is  0.96  square  foot  per  kilowatt  of  this  capacity.  The  second 


FIG.  39. — Power-house  on  Payette  River,  Idaho. 

station  with  vertical  units  at  Niagara  Falls  has  a  capacity  of  41,250  kilo- 
watts in  eleven  generators  on  vertical  shafts,  and  its  floor  area  amounts 
to  0.86  square  foot  per  kilowatt;  narrow  impulse- wheels  of  large  diameter 
tend  to  economy  of  floor  space,  as  in  Electra  station,  where  the  room 
containing  wheels  and  generators  has  an  area  of  only  0.83  square  foot 
per  unit  of  its  10,000  kilowatts  capacity.  At  the  Colgate  plant,  where 
the  total  rating  of  generators  is  11,250  kilowatts,  the  floor  area  under 
wheels  and  generators  is  almost  exactly  one  square  foot  per  kilowatt. 
The  Santa  Ana  station,  with  a  total  capacity  of  3,000  kilowatts,  has 
1.52  square  feet  of  floor  area  for  each  unit  of  capacity.  This  last  figure 
may  be  compared  with  the  1.72  square  feet  per  kilowatt  of  generator 


102     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


rating  for  the  4,8oo-kilowatt  station  at  Red  Bridge  and  the  1.75  square 
feet  per  unit  of  capacity  in  the  8oo-kilowatt  plant  at  Birchem  Bend. 

All  types  of  water-power  stations  with  direct-connected  wheels  and 
generators  have  much  smaller  floor  areas  per  unit  capacity  than  do 
steam-power  stations  with  direct-connected  horizontal  units.  Thus, 
the  modern  steam-driven  station  at  Portsmouth,  N.  H.,  has  a  plan  area 
in  engine-  and  boiler-rooms  of  16,871  square  feet,  and  its  total  capacity 
in  four  direct-connected  units  is  4,400  kilowatts,  so  that  the  area 
amounts  to  3.82  square  feet  per  kilowatt  rating  of  its  generators.  Of 
this  area  about  46  per  cent  is  in  the  boiler-room. 

FLOOR  DIMENSIONS  FOR  DIRECT-CONNECTED,  HORIZONTAL  WATER-WHEELS  AND 
GENERATORS  AT  ELECTRIC  STATIONS. 


Station. 

Feet  Long. 

Feet  Wide. 

Number 
of 
Generators. 

Total 
Kilowatt 
Capacity. 

^Niagara  No  2 

496 
1,368 

III 

22$ 
141 
j  140 
1  106 
127 
67-5 

(      62 

t  50 
56.6 

(        14-4 

•<    inside,  but 
(                 squ 

72 

IOO 

40 
40 
5° 

?l 

22  J 
36 

"l 

:34 

119.66  } 

minus  360   V 
are  feet.        ) 

II 
80 
7 
5 
10 
6 

4 

4 
4 

2 
2 

5 

41,250 
32,000 
11,250 

10,000 

7»5°° 
4,800 

3,000 

3,000 
2,000 

1,300 
800 

4,400 

Sault  Ste.  Marie 

Colgate  .     * 

Electra  .  . 

Caiion  Ferry  

Red  Bridge 

Apple  River  

Santa  Ana  River  
Great  Falls.  . 

Garvin's  Falls 

Birchem  Bend 

Portsmouth     (steam- 
driven) 

*Vertical  wheel  shafts. 

Some  of  these  dimensions  apply  to  the  inside  and  some  to  the  outside  of  stations. 
Some  small  projections  are  not  included. 


CHAPTER  IX. 

ALTERNATORS  FOR  ELECTRICAL  TRANSMISSION. 

DYNAMOS  in  the  generating  station  of  an  electric  transmission  system 
should  be  so  numerous  that  if  one  of  them  is  disabled  the  others  can  carry 
the  maximum  load.  If  only  two  generators  are  installed,  it  is  thus  desira- 
ble that  each  be  large  enough  to  supply  the  entire  output,  so  that  the 
dynamo  capacity  exceeds  the  greatest  demand  on  the  station  by  100  per 
cent.  To  avoid  so  great  excess  of  dynamo  capacity  it  is  common  prac- 
tice to  install  more  than  two  generators. 

Other  considerations  also  tend  to  increase  the  number  of  dynamos 
in  the  generating  station  of  a  transmission  system.  Thus  one  transmis- 
sion line  may  be  devoted  exclusively  to  lighting,  another  to  stationary 
motors,  and  a  third  to  electric  railway  service;  and  it  may  be  desirable 
that  each  line  be  supplied  by  an  independent  dynamo  to  avoid  any  effect 
of  fluctuations  of  railway  or  motor  load  on  the  lighting  system. 

At  the  generating  station  of  the  transmission  system  that  supplies 
electric  light  and  power  in  Portland,  Me.,  the  idea  of  independent  units 
has  been  carried  out  with  four  5oo-kilowatt  dynamos,  each  driven  by  a 
pair  of  wheels  fed  with  water  through  a  separate  penstock  from  the  dam. 
Each  of  these  dynamos  operates  one  of  the  four  independent  transmission 
circuits.  Where  a  number  of  water-power  stations  feed  into  a  single 
sub-station  the  requirement  that  each  generating  station  have  its  capacity 
divided  up  among  quite  a  number  of  dynamos  may  not  exist,  since  one 
station  may  be  entirely  shut  down  for  repairs  and  the  load  carried  mean- 
time by  the  other  stations.  A  good  illustration  of  this  point  may  be  seen 
at  Manchester,  where  a  single  sub-station  receives  energy  transmitted 
from  four  water-power  plants.  At  one  of  these  plants  the  entire  capac- 
ity of  1,200  kilowatts  is  in  a  single  generator. 

The  foregoing  considerations  as  to  the  number  of  dynamos  apply 
with  equal  force  to  both  steam-  and  water-driven  stations,  but  other 
factors  tend  to  increase  the  number  of  dynamos  in  water-power  plants 
where  the  head  of  water  is  comparatively  small.  This  tendency  is  due 
to  the  fact  that  the  peripheral  speeds  of  pressure  turbine  water-wheels 
should  be  about  twenty-five  per  cent  less  than  the  velocity  at  which  water 

103 


104     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


ALTERNATORS  FOR  TRANSMISSION.  105 

would  issue  from  an  opening  under  the  head  of  water  at  which  these 
wheels  operate  in  order  to  secure  high  efficiency.  This  velocity  of 
water  and  therefore  the  peripheral  speed  of  pressure  turbine  wheels  va- 
ries with  the  square  root  of  the  head  of  water. 

Since  the  peripheral  speed  of  turbines  is  thus  determined  by  the  heads 
of  water  under  which  they  operate,  and  since  the  diameters  of  turbines 
must  increase  with  their  capacities,  the  rate  of  revolution  for  pressure 
turbines  under  any  given  head  decreases  as  the  power  goes  up.  For  this 
reason  it  is  often  desirable  to  use  a  larger  number  of  dynamos  in  a  water- 
power  plant  than  would  otherwise  be  required  in  order  to  avoid  very  low 
speeds  of  revolution  on  the  direct-connection  to  the  turbines.  A  notable 
illustration  of  this  practice  exists  in  the  great  water-power  plant  of  the 
Michigan-Lake  Superior  Power  Company,  at  Sault  Ste.  Marie,  Mich., 
where  a  generating  capacity  of  32,000  kilowatts  is  divided  up  between 
80  dynamos  of  400  kilowatts  each.  The  head  of  water  available  at  the 
pressure  turbines  in  this  plant  is  about  16  feet,  and  their  speed  is  180 
revolutions  per  minute.  In  order  to  obtain  even  this  moderate  speed 
under  the  head  of  16  feet  it  was  necessary  to  select  turbines  of  only  140 
horse-power  each.  Four  of  these  turbines  are  mounted  on  each  shaft 
that  drives  a  4oo-kilowatt  dynamo,  direct-connected,  so  that  there  are 
320  wheels  in  all.  Had  a  smaller  number  of  wheels  been  employed  to 
yield  the  total  power  their  speed  and  that  of  direct-connected  dynamos 
must  have  been  less  than  180  revolutions  per  minute.  As  the  cost  of 
dynamos  increases  with  very  low  speeds  it  is  often  cheaper  to  install  a 
larger  number  of  dynamos  at  a  higher  speed  than  a  smaller  number 
at  a  lower  speed  for  a  given  total  capacity. 

The  use  of  a  larger  number  of  units  than  would  otherwise  be  necessary 
in  order  to  avoid  a  very  low  speed  is  further  illustrated  by  the  7,500- 
kilowatt  plant  of  the  Missouri  River  Power  Company,  «it  Canon  Ferry, 
Mont.  This  capacity  is  made  up  of  ten  generators,  each  rated  at  750 
kilowatts  and  direct-connected  to  a  pair  of  pressure  turbine  wheels  oper- 
ating at  157  revolutions  per  minute,  under  a  head  of  about  32  feet. 

Under  comparatively  high  heads  of  water  pressure  turbines  operate 
at  speeds  that  are  ample  for  direct-connection  to  even  the  largest  dy- 
namos. 

Thus  in  the  Niagara  Falls  plant,  where  the  head  of  water  is  136  feet, 
each  pair  of  turbines  drives  a  direct-connected  dynamo  of  3,750  kilowatts 
at  250  revolutions  per  minute.  In  the  rare  case  where  the  power  to  be 
developed  is  so  great  that  the  number  of  generators  necessary  to  give 
security  and  reliability  to  the  service  leaves  each  generator  with  a  capac- 


io6     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


ALTERNATORS  FOR  TRANSMISSION. 


107 


ity  larger  than  is  desirable  for  structural  reasons,  the  number  must  be 
increased  simply  to  reduce  the  size  of  each  generator.  Such  a  state  of 
facts  existed  at  Niagara  Falls,  where  the  first  station  contains  ten 
dynamos  of  3,750  kilowatts  each,  and  the  second  station  contains  eleven 
units  of  like  capacity. 

In  the  greater  number  of  transmission  systems  the  generators  are 
direct-connected  to  either  steam-engines  or  water-wheels,  and  their 
speeds  of  rotation  are  largely  determined  by  the  requirements  of  these 
prime  movers.  Steam-engines  can  be  designed  with  some  regard  to  the 
desirable  speeds  for  direct-connection  to  dynamos,  but  water-wheels  are 


FIG.  42.— 10,000  H.  P.  12,000  Volt  Generator  in  Canadian  Power-house  at  Niagara  Falls. 

less  flexible  in  this  particular.  Each  type  of  wheel  has  its  peripheral 
speed  mainly  determined  by  the  head  of  water  under  which  it  may  be 
required  to  operate,  and  variation  from  this  speed  means  serious  loss  of 
efficiency. 

Under  heads  of  much  more  than  100  feet  pressure  turbines  oper- 
ate at  rather  high  speeds  in  all  except  very  large  sizes.  It  is  much 
the  more  common  to  see  water-wheels  at  a  lower  speed  belted  to  dyna- 
mos at  a  higher  speed;  but  in  some  instances,  as  at  the  lighting  plant 
of  Spokane,  Wash.,  wheels  of  a  higher  speed  are  belted  to  dynamos 
of  a  lower  speed.  Another  plan  by  which  moderate  dynamo  speeds  are 
obtained  with  water-wheels  under  rather  high  heads  mounts  a  dynamo  at 
each  end  of  the  shaft  of  a  large  turbine  or  pair  of  turbines.  This  plan  is 
followed  at  the  plant  of  the  Royal  Aluminum  Company,  Shawinigan 


io8     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Falls,  Quebec,  where  there  are  two  pairs  of  horizontal  turbine  wheels, 
each  pair  developing  3,200  horse-power  under  a  head  of  125  feet,  and 
driving  a  dynamo  direct-coupled  on  each  end  of  its  shaft.  Where  ver- 
tical wheels  are  employed  it  is  sometimes  more  desirable  to  drive  some 
standard  type  of  dynamo  with  horizontal  shaft  by  means  of  bevel  gears 
than  to  design  a  special  dynamo  to  mount  directly  on  the  vertical  shaft. 
This  latter  plan  is  warranted  in  very  large  work  like  that  at  two  of  the 
Niagara  Falls  generating  stations,  where  the  twenty-one  3,7 5o-kilowatt 
dynamos  are  direct-connected,  each  on  the  vertical  shaft  of  a  turbine. 
This  type  of  connection  is  not  one  that  will  be  frequently  followed,  but 
at  one  other  point — Portland,  Ore. — each  dynamo  is  mounted  directly 
on  the  shaft  of  its  vertical  turbine  wheel. 

Where  water-wheels  must  operate  under  heads  of  several  hundred 
feet,  it  is  usually  necessary  to  abandon  pressure  turbines  and  to  adopt 
one  of  the  types  of  impulse-wheels.  In  this  class  of  wheels  the  periph- 
eral speed  of  highest  efficiency  is  only  one-half  the  spouting  velocity  of 
the  water  under  any  particular  head.  This  gives  the  impulse- wheels 
about  two-thirds  the  peripheral  speed  of  pressure  turbines  of  equal 
diameter  and  consequently  about  two-thirds  as  many  revolutions  per 
minute.  But  as  the  water  may  be  applied  at  one  or  more  points  on  the 
circumference  of  an  impulse-wheel,  as  desired,  such  wheels  may  have 
much  greater  diameters  than  pressure  turbines  for  equal  power  under  a 
given  head. 

These  properties  of  low  peripheral  speed,  as  to  head  and  great  diam- 
eter, as  to  power  developed,  fit  impulse-wheels  for  direct-connection  to 
dynamos  where  great  heads  of  water  must  be  employed,  and  they  are 
generally  used  in  such  cases.  This  is  particularly  true  for  the  Pacific 
coast,  where  water-powers  depend  more  on  great  heads  than  on  large 
volumes.  In  the  generating  plant  of  the  Bay  Counties'  Power  Company, 
at  Colgate,  Cal.,  the  dynamos  are  direct-connected  to  impulse-wheels 
that  operate  under  a  head  of  700  feet.  The  three  2,250-kilowatt  dy- 
namos in  this  plant  are  each  mounted  on  a  wheel  shaft  operating  at  285 
revolutions  per  minute,  and  each  of  the  four  i,i25-kilowatt  dynamos  is 
direct-driven  by  an  impulse-wheel  at  400  revolutions  per  minute. 
At  the  Electra,  Cal.,  plant  of  the  Standard  Electric  Company  the 
impulse-wheels  operate  at  240  revolutions  per  minute  under  a  head 
of  1,450  feet.  Each  of  the  five  pairs  of  these  wheels  drives  a  2,000- 
kilowatt  generator,  direct-connected.  As  the  head  of  water  at  these 
wheels  is  1,450  feet,  its  spouting  velocity  is  about  300  feet  per  second, 
or  18,000  feet  per  minute.  Each  wheel  is  eleven  feet  in  diameter,  so 


ALTERNATORS  FOR  TRANSMISSION. 


109 


no    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


ALTERNATORS  FOR  TRANSMISSION. 


in 


that  a  speed  of  240  revolutions  per  minute  gives  the  periphery  a  little 
less  than  9,000  feet  per  minute,  or  about  one-half  of  the  spouting  velocity 
of  the  water.  These  two  great  plants  are  excellent  illustrations  of  the 


\         / 

FIG.  5irt.    Plan  and  Elevation  of  Water  Wheels  and  Generators  at  Power  Station  on 
Burrard  Inlet,  near  Vancouver,  B.  C. 

way  in  which  impulse- wheels,  under  great  heads,  may  be  given  speeds 
that  are  suitable  for  direct-connected  dynamos. 

Three  types  of  alternators,  the  revolving  armature,  the  revolving 


ii2    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

magnet,  and  the  inductor,  are  used  in  the  generating  plants  of  electric 
transmission  systems. 

Revolving  armatures  are  used  in  the  dynamos  of  comparatively  few 
transmission  systems  and  hardly  at  all  in  those  of  recent  date.  The  pre- 
vailing type  of  alternator  for  transmission  work  is  that  with  internal 
revolving  magnets  and  external  stationary  armature.  This  type  is  em- 
ployed in  the  great  water-power  plants  at  Canon  Ferry,  Mont. ;  Sault  Ste. 
Marie,  Mich.,  and  for  all  of  the  generators  installed  in  the  later  Niagara 
Falls  plants.  For  the  sixteen  earlier  vertical  generators  at  Niagara  Falls 


I       FIG.  46.— Elevations  of  Water-wheels  and  Generators  at  Power-station  on  Burrard  Inlet, 

near  Vancouver,  B.  C. 

the  revolving  magnets  are  external  to  the  stationary  armatures,  but  this 
construction  has  the  disadvantage  of  high  first  cost  and  inaccessibility  of 
the  internal  armature,  and  is  not  likely  to  be  often  adopted  elsewhere. 

Inductor  alternators  are  those  in  which  both  the  armature  and  mag- 
net coils  are  stationary  and  only  a  suitable  structure  of  iron  revolves;  they 
are  employed  in  a  comparatively  small  number  of  transmission  systems, 
but  this  number  includes  some  of  the  largest  plants.  The  seven  alterna- 
tors in  the  Colgate,  Cal.,  plant  aggregating  11,250  kilowatts  capacity,  and 
the  five  alternators  in  the  plant  at  Electra  in  the  same  State,  with  a  capac- 
ity of  10,000  kilowatts,  are  all  of  the  inductor  type.  As  more  commonly 
constructed  the  magnet  winding  of  the  inductor  alternator  consists  of 
only  one  or  two  very  large  coils,  which  are  in  some  cases  as  much  as  ten 
feet  in  diameter.  The  repair  of  these  large  magnet  coils  seems  to  pre- 
sent a  more  serious  problem,  in  case  of  accident,  than  the  repair  of  the 
small  coils  used  on  interval,  revolving  magnets.  As  far  as  satisfactory 


ALTERNATORS  FOR  TRANSMISSION.  113 

operating  qualities  are  concerned,  inductor  alternators  and  those  with 
revolving  magnets  seem  to  be  on  an  equality,  but  for  structural  reasons 
inductor  alternators  will  probably  be  built  less  freely  in  the  future  than 
in  the  past. 

Nearly  all  long  transmissions  are  now  carried  out  with  either  two-  or 
three-phase  current.  The  most  notable  two-phase  installation  is  that  at 
Niagara  Falls,  where  the  original  ten  generators,  as  well  as  the  eleven 
dynamos  later  added  in  two  of  the  large  plants,  are  all  of  the  two-phase 
type.  At  Canon  Ferry,  Mont.,  the  first  four  of  the  75o-kilowatt  genera- 


FIG.  47.— Interior  of  Power-house  at  Garvin's  Falls  on  the  Merrimac  River. 

tors  were  two-phase,  but  the  six  machines  of  like  capacity  installed  later 
are  three-phase.  In  the  latest  plants  of  large  capacity  or  involving  very 
long  transmissions  three-phase  machines  have  been  generally  employed. 
This  is  true  of  the  Colgate  and  Electra  plants  in  California,  and  of  that 
at  Sault  Ste.  Marie,  Mich. 

As  to  frequency,  existing  practice  extends  all  the  way  from  133  cycles 
per  second  on  the  lines  at  Marysville,  Cal.,  down  to  only  15  cycles  on  the 
transmission  for  the  Washington  &  Baltimore  Electric  Railway. 

More  common  practice  ranges  between  25  and  60  cycles.  Niagara 
Falls  saw  the  first  great  plant  installed  for  25  cycles,  but  others  of  that 
.8 


ii4     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


ALTERNATORS  FOR  TRANSMISSION. 


frequency  are  now  engaged  in  the  supply  of  light  and  power  for  general 
distribution.  For  transmission  to  electric  railway  lines  a  frequency  of 
25  cycles  has  been  and  is  being  widely  used,  prominent  examples  of 


which  may  be  seen  in  the  New  Hampshire  traction,  the  Berkshire,  and 
the  Albany  &  Hudson  systems. 

The  strong  feature  of  a  system  at  25  cycles  is  that  it  is  well  suited  to 
the  supply  of  continuous  currents  through  rotary  converters  with  reason- 
able numbers  of  poles,  armature  slots,  and  commutator  bars. 


n6    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

On  the  other  hand,  the  cost  of  transformers  is  greater  with  current  at 
25  cycles  per  second  than  with  a  higher  frequency,  and  'this  current  is 
only  just  bearable  for  incandescent  lighting  and  quite  unsuited  for  arc 


lamps,  because  of  the  fluctuating  character  of  the  light  produced.  At  15 
cycles  per  second  a  current  can  be  employed  for  incandescent  lighting 
with  satisfactory  results  only  by  means  of  some  special  devices,  as  lamps 
with  very  thick  filaments,  to  avoid  the  flicker.  Very  low  fluctuations  cut 


ALTERNATORS  FOR  TRANSMISSION. 


117 


down  undesirable  effects  in  the  way  of  inductance  and  resonance,  but 
these  effects  can  be  avoided  to  a  large  degree  in  other  ways. 

Where  power  is  the  most  important  element  in  the  service  of  an  elec- 
tric water-power  and  transmission  system  there  is  a  decided  tendency  to 
adopt  a  rather  small  number  of  periods  for  the  system,  even  at  some  dis- 
advantage as  to  lighting  facilities.  This  is  illustrated  by  the  transmis- 
sion from  St.  Anthony's  Falls,  Minn.,  at  35  cycles,  from  Canon  City  to 
Cripple  Creek,  Col.,  at  30  cycles,  by  the  Sault  Ste.  Marie  plant  of  32,000 
kilowatts  at  30  cycles,  as  well  as  by  the  two  Niagara  Falls  plants  of 
78,750  kilowatts  at  25  cycles. 

Where  the  main  purpose  of  a  transmission  system  is  the  supply  of 
light  and  power  for  general  distribution,  sixty  periods  per  second  are 


g 

,00- 
—90- 

, 

-90- 

9 

j/ 

•^ 



—J               — 

| 

w  
^ 

^ 

5*- 

^.  •— 

• 

—70 
-60 

/ 

I 

/ 

ii 

/ 

/ 

LO£ 

±1 

\ 

1 
13< 
1M 

id      Eff. 
C~      72. 
?=      82.8 
'  =     87.2 
=     89.2 
=     90.0 
'=•     90.5 

50_ 

Lo 

$ 

i 
1 
1, 
1J 
.,2300 
;or  on 

ad     Eff. 
K>    77.3 
^=-86.25 
K-     89.4 
=    91.0 
<  =     91.6 
4-    91.8 
Volts,  450"E.: 
both  Machin 

I    i 

fficienc 

^  from 

EtlieSei 

cy  froi 





-20 
-10 
—  0 

1 

1  Output-  800  K.W..2300  Volts,  450  R  P  Jtt 
1    100%-power  Factor  on  both  Machines 

Outp 

10     loa 

it-lOi 

trpow 

(5K.-W 
sr  Fac 

J.M. 

OB 

r 

] 

i 

<    i    i  c 

fi       1 

,  ,L 

1  j 

(      > 

d~£] 

K       1 

* 

FIG.  51.— Efficiency  Curves  for  Motor  Generators  at  Montreal  Sub-station  of  the 
Shawinigan  Transmission  Line. 

adopted  as  the  standard  in  many  cases.  This  number  of  periods  in 
comparison  with  a  smaller  one  tends  to  increase  the  cost  of  rotary  con- 
verters but  decreases  the  cost  of  transformers,  and  is  suitable  for  both 
incandescent  and  arc  lighting. 

Few,  if  any,  transmission  systems  have  recently  been  installed  for 
frequencies  above  sixty  cycles,  and  the  older  plants  that  worked  at  higher 
figures  have  in  most  cases  been  remodelled. 

During  the  past  decade  the  voltages  of  alternators  have  been  greatly 


n8     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


increased,  but  have  not  caught  up  with  the  demand  for  high  pressures 
on  long-transmission  lines.  Ten  years  ago  when  the  first  long  transmis- 
sions were  going  into  operation  2,000  volts  was  considered  high  for  an 
alternator.  As  this  voltage  is  too  low  for  economy  of  conductors  longer 
than  three  or  four  miles,  the  important  early  transmissions  were  all  car- 
ried out  with  the  aid  of  step-up  transformers  at  generating  stations.  The 

ALTERNATORS  IN  TRANSMISSION  SYSTEMS. 


Location  of  System. 

Number  at 
Plant. 

Kilowatts 
Each. 

Alternator 
Voltage. 

* 
i 

PH 

J 
I 

0 

pj 

Q,  fcjO 

"o 

Method  of 
Connections. 

Niagara  Falls  *  
Niagara  Falls  *  . 

16 

5" 

3>75° 
37CO 

2,300 

2   7OO 

2 
2 

25 

2C. 

250 

External 
revolving 
Internal 

Direct 

Colgate  to  Oakland.  . 
Colgate  to  Oakland.  . 
Electra  to  S.Francisco 
Portsmouth  to  Pelh'm 
Portsmouth  to  Pelh'm 
Virginia  City 

3 
4 

5 

i 

2 

2 

2,250 
1,125 

2,000 
2,000 

1,000 
7C.O 

2,400 
2,400 

13,200 
13,200 

coo 

3 
3 
3 
3 
3 

60 
60 
60 
25 
25 
60 

285 
400 
240 
83-3 
94 

4OO 

Inductor 

Internal 
« 

External 

Ogden  &  Salt  Lake  .  . 
Chaudiere  Falls  
Yadkin  River  Falls  .  . 
Lewiston,  Me.  . 

5 

2 
2 

750 
750 
750 

7^0 

2,300 
10,500 
12,000 
10,000 

3 
3 
3 
? 

60 

66.6 
66 
60 

300 
400 
1  66 
180 

Internal 

Farmington  River     ) 
to 
Hartford,  Conn  ) 
Canon  Ferry  to  Butte 
Apple  Riv.  to  St.  Paul 
Edison  Co.,  L.Angeles 
Madrid  to  Bland  
Canon  City  to  Cripple 
Creek 

2 
2 
IO 

4 
4 

2 

750 
600 

750 

75° 
700 
600 

500 
500 
500 
800 

75° 
605 

coo 

3 

2 

3 
3 
3 
3 

•2 

60 
60 
60 
60 

60 

157 

300 

90 

:: 

Sault  Ste.  Marie  
St.  Hyacinthe,  Que.  .  . 
Great  Falls  to  Port- 
land, Me.  .  . 

80 

3 

400 
1  80 

coo 

2,400 
2,500 

10,000, 

3 
3 

•2 

3° 
60 

60 

1  80 
600 

M 

*  Niagara  Falls  Power  Company. 

practice  then  was,  and  to  a  large  extent  still  is,  to  design  the  alternators 
for  a  transmission  with  a  voltage  well  suited  to  their  economical  construc- 
tion, and  then  give  the  step-up  transformers  any  ratio  necessary  to  attain 
the  required  line  voltage. 

Thus  in  the  two  water-power  plants  connected  with  the  electrical 
supply  system  of  Hartford,  Conn.,  the  alternators  operate  at  500  volts 
with  transformers  that  put  the  line  voltage  up  to  10,000.  In  the  station 


ALTERNATORS  FOR  TRANSMISSION. 


119 


on  Apple  River  that  supplies  the  lighting  system  of  St.  Paul,  Minn.,  the  al- 
ternators operate  at  800  volts,  and  this  is  raised  to  25,000  volts  for  the 
line.  At  Canon  Ferry  the  alternator  voltage  of  500  is  multiplied  by  100 
in  the  transformers  giving  50,000  on  the  line. 


Electric  Roads 

High  Tension  Lines-. 
Rotary  Stations 


F.G.  52.— Transmission  Line  of  New  Hampshire  Traction  Company. 

Where  the  generating  station  of  a  transmission  system  is  located 
close  to  a  part  of  its  load  the  alternators  are  given  a  voltage  suitable  for 
distribution,  say  about  2,400,  and  any  desired  pressure  on  the  line  is 
then  obtained  by  means  of  step-up  transformers.  Two  of  the  Niagara 


120    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Falls  plants  are  an  illustration  of  this  practice,  the  voltage  of  all  the 
alternators  there  being  2,200,  which  is  raised  to  22,000  for  the  transmis- 
sion of  a  part  of  the  energy  to  Buffalo.  A  similar  practice  is  followed  in 
the  water-power  plant  at  Ogden,  where  the  generators  furnish  current 
at.  2,  300  volts  for  local  distribution,  and  transformers  raise  the  pressure 
to  26,000  volts  for  the  transmission  to  Salt  Lake  City.  In  the  32,000- 
kilowatt  plant  at  Sault  Ste.  Marie,  Mich.,  the  alternators  operate  at 
2,400  volts  and  a  large  part  of  their  load  is  local,  but  this  voltage  will  no 
doubt  be  raised  by  transformers  when  transmission  lines  are  operated. 

For  generating  stations  that  carry  little  or  no  local  loads  the  cost  of 
transformers  can  be  saved  if  the  generators  develop  the  voltage  required 
on  the  transmission  lines.  This  possible  saving  has  led  to  the  develop- 
ment of  alternators  that  generate  voltages  as  high  as  15,000  in  their 
armature  coils.  Such  alternators  have  stationary  armatures  in  all  cases 
and  are  of  either  the  revolving  magnet  or  inductor  type. 

At  the  present  time  many  transmission  systems  in  the  United  States 
operating  at  10,000  or  more  volts  develop  these  pressures  in  the  arma- 
ture coils  of  their  alternators,  and  the  number  of  such  systems  is  rapidly 
increasing.  It  is  now  the  rule  rather  than  the  exception  to  dispense 
with  step-up  transformers  on  new  work  where  the  line  voltage  is  any- 
thing under  15,000.  Perhaps  the  longest  transmission  line  now  in 
regular  operation  with  current  from  the  armature  coils  of  an  -alternator 
is  that  at  13,200  volts  between  the  generating  station  at  Portsmouth  and 
one  of  the  sub-stations  of  the  New  Hampshire  Traction  system  at  Pel- 
ham,  a  distance  of  forty-two  miles. 

In  at  least  one  transmission  system  now  under  construction,  that  of 
the  Washington,  Baltimore  &  Annapolis  Electric  Railway,  the  voltage  of 
generators  to  supply  the  line  without  the  intervention  of  step-up  trans- 
formers will  be  15,000. 

The  company  making  these  alternators  is  said  to  be  ready  to  supply 
others  that  generate  20,000  volts  in  the  armature  coils  whenever  the 
demand  for  them  is  made.  In  quite  a  number  of  cases  alternators  of 
about  13,000  volts  have  been  installed  for  transmissions  along  electric 
railway  lines. 


Systems  Using  High-voltage  Alternators. 

Electrical  Development  Co.  of  Ontario,  Niagara  Falls  .................  12,000 

Lighting  and  Street  Railway,  Manchester,  N.  H  ......................  10,000 

Lighting  and  Street  Railway,  Manchester,  N.  H  ......................  12,500 

Lighting  and  Power,  Portland,  Me  ...............................  10,000 

Lighting  and  Power,  North  Gorham,  Me  .............................  10,000 

Mallison  Power  Co.,  Westbrook,  Me  ................................  10,000 

Lighting  and  Power,  Lewiston,  Me  ......     ..........................  10,000 


ALTERNATORS  FOR  TRANSMISSION.  121 

Systems  Using  High-voltage  Alternators.  Voltages.1" 

Electric  Railway,  Portsmouth,  N.  H 13,200 

Electric  Railway,  Pittsfield,  Mass 12,500 

Ludlow  Mill?,  Ludlow,  Mass 13,200 

Electric  Railway,  Boston  to  Worcester,  Mass 13,200 

Electric  Railway,  Albany  &  Hudson,  N.  Y 12,000 

Empire  State  Power  Co.,  Amsterdam,  N.  Y 12,000 

Lehigh  Power  Co.,  Easton,  Pa 12,000 

Hudson  River  Power  Co.,  Mechanicsville,  N.  Y 12,000 

Light  and  Power,  Anderson,  S.  C 11,000 

Fries  Mfg.  Co.,  Salem,  N.  C 12,000 

Light  and  Power,  Ouray,  Col 12,000 

Washington  &  Baltimore  Electric  Railway 15,000 

Canadian  Niagara  Power  Co.,  Niagara  Falls 12,000 

Ontario  Power  Co.,  Niagara  Falls 12,000 

This  list  of  high-voltage  alternators  is  not  intended  to  be  exhaustive, 
but  serves  to  indicate  their  wide  application.  If  such  alternators  can  be 
purchased  at  a  lower  price  per  unit  of  capacity  than  alternators  of  low 
voltage  plus  step-up  transformers,  there  is  an  apparent  advantage  for 
transmission  systems  in  the  high-voltage  machines.  This  advantage  may 
rest  in  part  on  a  higher  efficiency  in  the  alternators  that  yield  the  line 
voltage  than  in  the  combination  of  low-voltage  alternators  plus  step-up 
transformers.  It  is  not  certain,  however,  that  depreciation  and  repairs 
on  the  generators  of  high  voltage  will  not  be  materially  greater  than  the 
like  charges  on  generators  of  low  voltage,  and  some  advantage  in  price 
should  be  required  to  cover  this  contingency. 

Just  how  far  up  the  voltage  of  alternators  can  be  pushed  for  practi- 
cal purposes  is  uncertain,  but  it  seems  that  the  limit  must  be  much 
below  that  for  transformers  where  there  is  ample  room  for  solid  insu- 
lation and  the  coils  can  be  immersed  in  oil.  The  use  of  generators  at 
10,000  volts  and  above  tends  to  lower  the  volts  per  mile  on  transmission 
lines,  because  it  seems  better  in  some  cases  to  increase  the  weight  of  line 
conductors  rather  than  to  add  step-up  transformers,  as  in  the  4 2 -mile 
transmission  from  Portsmouth  to  Pelham. 


CHAPTER  X. 

TRANSFORMERS  IN  TRANSMISSION  SYSTEMS. 

TRANSFORMERS  are  almost  always  necessary  in  long  electric  systems 
of  transmission,  because  the  line  voltage  is  greater  than  that  of  genera- 
tors, or  at  least  that  of  distribution.  As  transformers  at  either  generat- 
ing or  receiving  stations  represent  an  increase  of  investment  without  cor- 
responding increase  of  working  capacity,  and  also  an  additional  loss  in 
operation,  it  is  desirable  to  avoid  their  use  as  far  as  is  practicable.  In 
short  transmissions  over  distances  of  less  than  fifteen  miles  it  is  generally 
better  to  avoid  the  use  of  transformers  at  generating  stations,  and  in 
some  of  these  cases,  where  the  transmission  is  only  two  or  three  miles, 
it  is  even  more  economical  to  omit  transformers  at  the  sub-stations. 

Thus,  where  energy  is  to  be  transmitted  two  miles  and  then  applied 
to  large  motors  in  a  factory,  or  distributed  at  2,500  volts,  the  cost  of  bare 
copper  conductors  for  the  three-phase  transmission  line  will  be  only  about 
#6  per  kilowatt  of  line  capacity  at  2,500  volts,  with  copper  at  15  cents 
per  pound,  and  a  loss  of  5  per  cent  at  full  load.  The  average  loss  in  such 
a  line  will  probably  be  as  small  as  that  in  one  set  of  transformers  and  a 
line  of  higher  voltage.  Furthermore,  the  first  cost  of  the  2,5oo-volt 
generators  and  line  without  transformers  will  be  less  than  that  of  gener- 
ators and  line  of  higher  voltage  with  step-down  transformers  at  the  sub- 
station. 

As  generators  up  to  13,500  volts  are  now  regularly  manufactured,  it 
is  quite  common  to  omit  step-up  transformers  at  the  main  stations  of 
rather  short  transmission  systems.  This  practice  was  followed  in  the 
1 3, 500- volt  transmission  to  Manchester,  N.  H.,  the  10,000- volt  transmis- 
sion to  Lewiston,  Me.,  and  the  12,000- volt  transmission  to  Salem,  N.  C. 

In  most  transmission  over  distances  of  twenty-five  miles  or  more, 
step-up  transformers  at  generating  stations  as  well  as  step-down  trans- 
formers at  sub-stations  are  employed.  As  yet  the  highest  voltages  that 
have  been  put  into  practical  use  on  transmission  lines  (that  is,  50,000  to 
60,000)  are  much  below  the  pressures  that  have  been  yielded  by  trans- 
formers in  experimental  work.  These  latter  voltages  have  in  a  number 
of  instances  gone  above  100,000.  The  numbers  and  capacities  of  trans- 

122 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     123 


i24    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

formers  used  at  main  stations  vary  much  in  their  relation  to  the  numbers 
and  individual  capacities  of  generators  there.  In  some  cases  there  are 
three  times  as  many  transformers  as  three-phase  generators,  and  the 
capacity  of  each  transformer  is  either  equal  to  or  somewhat  greater  than 
one-third  of  the  capacity  of  each  generator. 

Thus  in  the  station  at  Spier  Falls  on  the  Hudson,  whence  power  is 
transmitted  to  Albany  and  other  cities,  the  number  of  step-up  trans- 
formers will  be  thirty  and  their  aggregate  capacity  will  be  24,014  kilo- 
watts, while  the  total  number  of  three-phase  generators  will  be  ten,  with 
a  combined  capacity  of  24,000  kilowatts.  Another  practice  is  to  give 
each  transformer  a  capacity  greater  than  one-third  of  that  of  the  three- 
phase  generator  with  which  it  is  to  be  connected,  and  make  the  total  num- 
ber of  transformers  less  than  three  times  as  great  as  the  number  of  gen- 
erators. An  example  of  this  sort  exists  in  the  station  on  Apple  River, 
whence  power  is  transmitted  to  St.  Paul.  This  station  contains  four 
three-phase  generators  of  750  kilowatts  each,  and  six  transformers  of 
500  kilowatts  each,  these  latter  being  connected  in  two  sets  of  three  each. 
The  use  of  three  transformers  for  each  three-phase  generator  instead  of 
three  transformers  for  each  two  or  three  generators,  tends  to  keep  trans- 
formers fully  loaded  when  in  use,  and  therefore  to  increase  their  effi- 
ciency. On  the  other  hand,  efficiency  increases  a  little  with  the  size  of 
transformers,  and  the  first  cost  per  unit  capacity  is  apt  to  be  less  the 
greater  the  size  of  each. 

Another  solution  of  the  problem  is  to  provide  one  transformer  for 
each  three-phase  generator,  each  transformer  being  wound  with  three 
sets  of  coils,  so  that  the  entire  output  of  a  generator  can  be  sent  into  it. 
This  practice  is  followed  at  the  Hochfelden  water-power  station,  whence 
power  is  transmitted  to  Oerlikon,  Switzerland,  also  in  the  water-power 
station  at  Grenoble,  France,  whence  energy  at  26,000  volts  is  transmitted 
to  a  number  of  factories.  With  three-phase  transformers  each  generator 
and  its  transformer  may  form  an  independent  unit  that  can  be  connected 
with  the  line  at  pleasure,  thus  tending  to  keep  transformers  at  full  load. 

Though  three-phase  transformers  are  much  used  in  Europe,  they 
have  thus  far  had  little  application  in  the  United  States.  Single-phase 
transformers  may,  of  course,  be  limited  in  number  to  that  of  the  three- 
phase  generators  with  which  they  are  used,  but  such  transformers  must 
regularly  be  connected  to  the  generators  and  line  in  groups  of  two  or  three. 
Such  an  equipment  was  provided  in  part  at  the  7,5oo-kilowatt  station  on 
the  Missouri  River  at  Canon  Ferry,  which  contains  ten  three-phase  gen- 
erators of  750  kilowatts  each.  The  transformers  at  this  station  include 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     125 

twelve  of  325  kilowatts  each,  connected  in  four  groups  of  three  each,  also 
six  transformers  of  950  kilowatts  each  which  are  also  connected  in  groups 
of  three.  Three  of  these  larger  transformers  have  a  capacity  of  2,850 
kilowatts,  or  nearly  equal  to  that  of  four  generators. 

With  two-phase  generators  single-phase  transformers  must  be  con- 
nected in  pairs,  and  it  is  common  to  provide  two  transformers  for  each 
generator.  Thus,  in  the  Rainbow  station  on  the  Farmington  River, 
whence  energy  is  transmitted  to  Hartford,  there  are  twro  generators  of  the 
two-phase  type  and  rated  at  600  kilowatts  each,  also  four  transformers 
rated  at  300  kilowatts  each. 

As  the  regulation  of  transformers  on  overloads  is  not  as  good  as  that 
of  generators,  it  seems  good  practice  to  give  each  group  of  transformers 
a  somewhat  greater  capacity  than  that  of  the  generator  or  generators 
whose  energy  is  to  pass  through  it.  This  plan  was  apparently  followed 
at  the  Canon  Ferry  station,  where  the  total  generator  capacity  is  7,500 
kilowatts  and  the  total  capacity  of  step-up  transformers  is  9,600  kilowatts. 
Each  group  of  the  325-kilowatt  transformers  there  has  a  capacity  of  975 
kilowatts,  while  each  generator  is  only  of  750  kilowatts.  Usually  the 
number  of  groups  of  transformers  at  a  two-phase  or  three-phase  generat- 
ing station  is  made  greater  than  the  number  of  transmission  circuits  sup- 
plied by  the  station,  for  some  of  the  reasons  just  considered.  When  this 
is  not  trie  case  it  is  commonly  desirable  in  any  event  to  have  as  many 
groups  of  step-up  transformers  as  there  are  transmission  circuits,  so  that 
each  circuit  may  be  operated  with  transformers  that  are  independent  of 
the  other  circuits. 

At  sub-stations  it  is  desirable  to  have  a  group  of  transformers  for  each 
transmission  circuit,  and  it  may  be  necessary  to  subdivide  the  trans- 
former capacity  still  further  in  order  to  keep  transformers  in  operation 
at  nearly  full  load,  or  to  provide  a  group  of  transformers  for  each  sort  of 
service  or  for  each  distribution  circuit.  All  of  the  transformers  at  a  sub- 
station should  have  a  total  capacity  at  least  equal  to  that  of  the  generators 
whose  energy  they  are  to  receive,  minus  the  losses  in  step-up  transformers 
and  the  line.  Transformers  at  sub-stations  do  not  necessarily  corre- 
spond in  number  or  individual  capacity  with  those  at  generating  stations, 
and  the  number  of  sub-station  transformers  bears  no  necessary  relation 
to  the  number  of  generators  by  which  they  are  fed. 

Two  transmission  circuits  extend  from  Canon  Ferry  to  a  sub-station 
at  Butte,  and  in  that  sub-station  there  are  six  transformers  divided  into 
two  groups  for  three-phase  operation,  each  transformer  being  rated  at 
950  kilowatts.  This  sub-station  equipment  thus  corresponds  to  only  the 


126     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

six  95o-kilowatt  transformers  in  the  generating  station,  because  the  four 
groups  of  smaller  transformers  there  are  used  to  supply  the  transmission 
line  to  Helena. 

In  the  sub-station  at  St.  Paul  that  receives  the  entire  output  of  the 
plant  on  Apple  River,  where  the  six  transformers  of  500  kilowatts  each 
are  located,  ten  transformers  receive  energy  from  two  three-phase  trans- 
mission circuits.  Six  of  these  transformers  are  rated  at  300  kilowatts 
each.  The  3oo-kilowatt  transformers  are  connected  in  two  groups  of 
three  each,  and  the  2oo-kilowatt  in  two  groups  of  two  each,  transforming 
current  from  three-phase  to  two-phase.  The  aggregate  capacity  of  the 
sub-station  transformers  is  thus  2,600  kilowatts,  while  that  of  transform- 
ers at  the  generating  station  is  3,000  kilowatts.  With  four  generators  at 
the  water-power  plant  there  are  ten  transformers  at  the  sub-station, 
where  all  the  energy,  minus  losses,  is  delivered. 

At  Watervliet,  where  one  of  the  several  sub-stations  of  the  system  with 
its  larger  generating  plant  at  Spier  Falls  is  located,  the  capacity  of  each 
transformer  is  1,000  kilowatts,  though  each  transformer  at  Spier  Falls 
has  a  rating  below  this  figure. 

In  the  sub-station  at  Manchester,  N.  H.,  that  receives  nearly  all  of 
the  energy  from  four  water-power  plants,  containing  eight  generators 
with  an  aggregate  capacity  of  4,030  kilowatts,  there  are  located  twenty- 
one  step-down  transformers  that  have  a  total  rating  of  4,200  kilowatts. 
These  twenty-one  transformers  are  fed  by  six  circuits,  of  which  five  are 
three-phase  and  one  is  two-phase.  A  part  of  the  transformers  supply 
current  to  motor-generators,  developing  5oo-volt  current  for  a  street  rail- 
way, and  the  remaining  transformers  feed  circuits  that  distribute  alter- 
nating current. 

From  these  examples  it  may  be  seen  that  in  practice  either  one  or 
more  groups  of  transformers  are  employed  in  sub-stations  for  each  trans- 
mission circuit,  that  the  total  number  of  these  transformers  may  be  just 
equal  to  or  several  times  that  of  the  generators  from  which  they  receive 
energy,  and  that  the  individual  capacities  of  the  transformers  range  from 
less  than  one-third  to  more  than  that  of  a  single  generator.  Groups  of 
transformers  at  a  main  station  must  correspond  in  voltage  with  that  of 
the  generators  in  the  primary  and  that  of  the  transmission  line  in  the 
secondary  windings.  Sub-station  transformers  receive  current  at  the  line 
voltage  and  deliver  it  at  any  of  the  pressures  desired  for  local  distribu- 
tion. Where  step-up  transformers  are  employed  the  generator  pressure 
in  nearly  all  cases  is  at  some  point  between  500  and  2,500  volts. 

At  the  Canon  Ferry  station  the  voltage  of  transformers  is  550  in 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     127 

in  the  primary  and  50,000  in  the  secondary  windings.  In  the  Colgate 
power-house,  whence  energy  is  transmitted  to  Oakland,  the  generator 
pressure  of  2,400  volts  is  raised  to  40,000  volts  by  transformers.  Gen- 
erator voltage  in  the  power-house  on  Apple  River  is  800  and  transform- 
ers put  the  pressure  up  to  25,000  for  the  line  to  St.  Paul.  Transformers 
at  the  Niagara  Falls  station  raise  the  voltage  from  2,200  to  22,000  for  the 
transmission  to  Buffalo. 

As  transformers  can  be  wound  for  any  desired  ratio  of  voltages  in 
their  primary  and  secondary  coils,  a  generator  pressure  that  will  allow 
the  most  economical  construction  can  be  selected  where  step-up  trans- 
formers are  employed.  In  general  it  may  be  said  that  the  greater  the 
capacity  of  each  generator,  the  higher  should  be  its  voltage  and  that  of 
the  primary  coils  of  step-up  transformers,  for  economical  construction. 
At  sub-stations  the  requirements  of  distribution  must  obviously  fix  the 
secondary  voltages  c-f  transformers. 

Weight  and  cost  of  transformers  depend  in  part  on  the  frequency  of 
the  alternating  current  employed,  transformers  being  lighter  and  cheaper 
the  higher  the  number  of  cycles  completed  per  second  by  their  current, 
other  factors  remaining  constant.  In  spite  of  this  fact  the  tendency  dur- 
ing some  years  has  been  toward  lower  frequencies,  because  the  lower 
frequencies  present  marked  advantages  as  to  inductive  effects  in  trans- 
mission systems,  the  distribution  of  power  through  induction  motors,  the 
construction  and  operation  of  rotary  converters,  and  the  construction  of 
generators.  Instead  of  the  133  cycles  per  second  that  were  common  in 
alternating  systems  when  long  transmissions  first  became  important, 
sixty  cycles  per  second  is  now  the  most  general  rate  of  current  changes 
in  such  transmission  systems.  But  practice  is  constantly  extending  to 
still  lower  frequencies.  The  first  Niagara  Falls  plant  with  its  twenty-five 
cycles  per  second  reached  the  lower  limit  for  general  distribution,  because 
incandescent  lighting  is  barely  satisfactory  and  arc  lighting  decidedly 
undesirable  at  this  figure. 

In  contrast  with  the  great  transmissions  from  Canon  Ferry  to  Butte, 
Colgate  to  Oakland,  and  Electra  to  San  Francisco,  which  operate  at  sixty 
cycles,  the  system  between  Canon  City  and  Cripple  Creek,  in  Colorado, 
as  well  as  the  great  plant  at  Sault  Ste.  Marie,  employs  thirty-cycle 
current,  and  the  lines  from  Spier  Falls  to  Schenectady,  Albany,  and 
Troy  are  intended  for  current  at  forty  cycles  per  second.  From  these 
examples  it  may  be  seen  that  the  bulk  and  cost  of  transformers  is  not 
the  controlling  factor  in  the  selection  of  current  frequency  in  a  trans- 
mission system. 


128    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


S3 

1 

l~        "S" 

u                  J 

J 

Air  Compressor 

D 


ooo 


Work  Room 


Cell  Room 


FIG.  54. — First  Floor  of  Saratoga  Sub-station. 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     129 

Transformers  used  at  either  generating  or  sub-stations  are  cooled 
by  special  means  in  many  cases. 

The  advantages  of  so-called  artificial  cooling  are  smaller  weight  and 
first  cost  in  transformers,  and  perhaps  longer  life  for  the  insulation  of 
windings.  For  these  advantages  a  small  increase  in  the  cost  of  opera- 
tion must  be  paid.  Station  transformers  are  usually  cooled  either  by 
forcing  air  through  their  cases  under  pressure,  or  else  by  passing  water 
through  pipes  in  the  oil  with  which  the  transformer  cases  are  filled.  If 
cooling  with  air-blast  is  adopted,  a  blower,  with  electric  motor  or  some 
other  source  of  power  to  operate  it,  must  be  provided.  Where  trans- 
formers are  oil-insulated  and  cooled  with  water  there  must  be  some  pres- 
sure to  maintain  the  circulation.  If  free  water  under  a  suitable  head 
can  be  had  for  the  cooling  of  transformers,  as  in  most  water-power  plants, 
the  cost  is  very  slight.  Where  water  must  be  purchased  and  pumped 
through  the  transformers  its  cost  will  usually  be  greater  than  that  of  cool- 
ing with  air-blast.  One  manufacturer  gives  the  following  as  approximate 
figures  for  the  rate  at  which  water  at  the  temperature  of  15°  centigrade 
must  be  forced  through  his  transformers  to  prevent  a  rise  of  more  than 
35°  centigrade  in  their  temperature,  probably  when  operating  under  full 
loads. 

Transformers— Kilowatts.    Gallons  per  minute. 

150  0-5 
400  .75 

400  i.oo 

1,000  1.5 
75  -37 

An  air-blast  to  cool  transformers  at  main  or  sub-stations  may  be  pro- 
vided in  either  of  two  ways.  One  plan  is  to  construct  an  air-tight  com- 
partment, locate  the  transformers  over  openings  in  its  top,  and  maintain 
a  pressure  in  the  compartment  by  means  of  blower-fans  that  draw  cool 
air  from  outside.  Such  an  arrangement  has  been  carried  out  at  the  sub- 
station in  Manchester,  N.  H.  The  basement  underneath  this  sub-sta- 
tion is  air-tight,  and  in  the  concrete  floor  over  it  there  are  twenty-seven 
rectangular  openings,  each  twenty-five  by  thirty  inches,  and  intended  for 
the  location  of  a  2oo-kilowatt  transformer.  Aggregate  transformer  capac- 
ity over  these  openings  will  thus  be  5,400  kilowatts.  Pressure  in  this 
basement  is  maintained  by  drawing  outside  air  through  a  metal  duct  that 
terminates  in  a  hood  on  the  outside  of  the  sub-station  about  nine  feet 
above  the  ground.  In  the  roof  of  this  sub-station  there  are  ample  sky- 
light openings  to  permit  the  exit  of  hot  air  that  has  been  forced  through 
the  transformers.  In  the  air-tight  basement  are  two  electric  motors  of 
9 


i3o    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

ten  horse-power  each,  connected  to  the  blower  that  maintains  the 
pressure.  It  may  be  noted  that  in  this  case  there  is  less  than  one-horse 
power  of  motor  capacity  for  each  200  kilowatts  capacity  in  transformers. 

Where  there  are  not  more  than  six  or  nine  transformers  to  be  cooled, 
it  is  common  practice  to  provide  a  separate  motor  and  blower  for  each 
group  of  three  transformers,  and  lead  the  air  directly  from  each  blower 
to  its  group  of  transformers  by  a  metal  duct,  thus  avoiding  the  necessity 
for  an  air-chamber.  In  such  cases  a  blower  giving  a  three-eighth-ounce 
air  pressure  per  square  inch  and  a  motor  of  one  horse-power  capacity  are 
generally  provided  for  each  group  of  three  transformers  rated  at  100  to 
150  kilowatts  each.  Where  cooling  with  air-blast  is  adopted,  oil-insula- 
tion cannot  be  carried  out  because  the  air  must  come  into  intimate  con- 
tact with  the  transformer  coils  and  core.  Both  oil-insulation  with  water 
cooling  and  dry  insulation  with  cooling  by  air-blast  have  been  widely 
used  in  transmission  systems  of  large  capacity  and  high  voltage. 

In  the  Colgate  plant,  where  the  line  pressure  is  40,000  volts,  the  700- 
kilowatt  transformers  are  oil-insulated  and  water-cooled,  and  this  is  also 
true  of  the  95o-kilowatt  transformers  in  the  5o,ooo-volt  transmission  be- 
tween Canon  Ferry  and  Butte.  On  the  other  hand,  the  transmission 
system  between  Spier  Falls,  Schenectady,  and  Albany,  carried  out  at 
26,500  volts,  includes  transformers  that  range  from  several  hundred  to 
1,000  kilowatts  each  in  capacity  and  are  all  air-cooled.  Either  a  water- 
cooled  transformer  or  one  cooled  by  air-blast  may  be  safely  overloaded 
to  some  extent,  if  the  circulation  of  air  or  water  is  so  increased  that  the 
overload  does  not  cause  heating  beyond  the  allowable  temperature. 

The  circulation  of  air  or  water  through  a  transformer  should  never 
be  forced  to  an  extent  that  cools  the  transformer  below  the  temperature 
of  the  air  in  the  room  where  it  is  located,  as  this  will  cause  the  condensa- 
tion of  water  on  its  parts. 

In  some  cases  it  is  desirable  that  means  for  the  regulation  of  trans- 
former voltages  through  a  range  of  ten  per  cent  or  more  each  way  from 
the  normal  be  provided.  This  result  is  reached  by  the  connection  of  a 
number  of  sections  at  one  end  of  the  transformer  winding  to  a  terminal 
board,  where  they  may  be  cut  in  or  out  of  action  at  will.  Regulation  is 
usually  desired,  if  at  all,  in  a  secondary  winding  of  comparatively  low 
voltage,  and  the  regulating  sections  generally  form  a  part  of  such  wind- 
ing, but  these  sections  may  be  located  in  the  primary  winding. 

In  order  to  keep  the  number  of  transformers  smaller  and  the  capacity 
of  each  larger  than  it  would  otherwise  be,  it  is  practicable  to  divide  the 
low-voltage  secondary  winding  of  each  transformer  into  two  or  more 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     131 

parts  that  have  no  electrical  connection  with  each  other.  These  different 
parts  of  the  winding  may  then  be  connected  to  distinct  distribution  lines 
or  other  services.  An  example  of  this  sort  exists  in  the  Hooksett  sub- 
station of  the  Manchester,  N.  H.,  transmission  system.  Three-phase 
current  at  about  11,000  volts  enters  the  primary  windings  of  three  trans- 
formers at  this  sub-station.  Each  of  these  transformers  has  a  single 
primary,  but  two  distinct  secondary  windings.  Three  of  these  second- 
aries, one  on  each  transformer,  are  connected  together  and  feed  a  rotary 
converter  at  about  380  volts,  three-phase.  The  other  three  secondary 
windings  are  connected  in  like  manner  to  a  second  rotary  converter. 
Each  of  these  transformers  is  rated  at  250  kilowatts,  and  each  rotary  is 
rated  at  300  kilowatts,  so  that  the  transformer  capacity  amounts  to  750 
kilowatts  and  that  of  the  converters  to  600  kilowatts,  giving  a  desirable 
margin  of  transformer  capacity  for  railway  service.  With  the  ordinary 
method  of  connection  and  windings,  six  transformers  of  125  kilowatts 
each  would  have  been  required  in  this  sub-station. 

High  voltage  for  transmission  lines  may  be  obtained  by  the  combina- 
tion of  two  or  more  transformers  with  their  secondary  coils  in  series. 
This  method  was  followed  in  some  of  the  early  transmissions,  as  in  that 
at  10,000  volts  to  San  Bernardino  and  Pomona,  begun  in  1891,  where 
twenty  transformers,  giving  500  volts  each,  were  used  with  their  high- 
voltage  coils  in  series.  Some  disadvantages  of  such  an  arrangement  are 
its  high  cost  per  unit  of  transformer  capacity  and  its  low  efficiency. 

In  a  single-phase  system  the  maximum  line  pressure  must  be  de- 
veloped or  received  in  the  coils  of  each  transformer,  unless  two  or  more 
are  connected  in  series.  This  is  also  true  as  to  either  phase  of  a  two- 
phase  system  with  independent  circuits.  In  three-phase  circuits  the  coils 
of  a  transformer  connected  between  either  two  wires  obviously  operate 
at  the  full  line  pressure.  The  same  result  is  reached  when  the  three 
transformers  of  a  group  are  joined  to  the  line  in  mesh  or  A  -fashion.  If 
the  three  transformers  of  a  group  are  joined  in  star  or  Y-fashion,  the  coils 
of  each  transformer  are  subject  to  fifty-eight  per  cent  of  the  voltage  be- 
tween any  two  wires  of  the  three-phase  line  on  which  the  group  is  connected. 
It  is  no  longer  the  practice  to  connect  two  or  more  transformers  in  series 
either  between  two  wires  of  a  two-phase  or  between  two  wires  of  a  three- 
phase  circuit,  because  it  is  cheaper  and  more  efficient  to  use  a  single  trans- 
former in  each  of  these  positions.  Where  very  high  voltage  must  be  de- 
veloped or  received  with  a  three-phase  system,  the  star  or  Y-connection 
of  each  group  of  three  transformers  has  the  advantage  of  a  lower  strain 
on  the  insulation  of  each  transformer  than  that  with  the  mesh  or  A  - 


132     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

grouping.  Thus  if  the  A -grouping  is  used,  the  line  pressure  equals 
that  of  each  transformer  coil,  but  if  the  Y-grouping  is  used  the  line 
voltage  is  1.73  times  that  of  each  transformer  coil. 

At  the  Colgate  power-house,  the  yoo-kilowatt  transformers  are  de- 
signed for  a  maximum  pressure  of  60,000  volts  on  the  three-phase  line 
when  Y-connected,  so  that  the  corresponding  voltage  is  34,675  in  their 
secondary  coils.  The  primary  coils  of  these  same  transformers  are  con- 
nected in  mesh  or  A -form  and  each  coil  operates  at  2,300  volts,  the 
generator  pressure. 

Transformers  are  in  some  cases  provided  with  several  sets  of  connec- 
tions to  their  coils  so  that  they  may  be  operated  at  widely  different  press- 
ures. Thus,  in  the  Colgate  plant,  each  transformer  has  taps  brought 
out  from  its  secondary  coils  so  that  it  can  be  operated  at  either  23,175, 
28,925,  or  34,675,  with  2,300  volts  at  its  primary  coil.  Corresponding  to 
the  three  voltages  named  in  each  secondary  coil  are  voltages  of  40,000, 
50,000,  and  60,000  on  a  three-phase  line  connected  with  three  of  these 
transformers  in  Y-fashion. 

The  mesh  or  A  -connection  is  used  between  the  coils  of  transformers 
on  some  transmission  lines  of  very  high  voltage.  The  950  kilowatt 
transformers  in  the  system  between  Canon  Ferry  and  Butte  illustrate  this 
practice,  being  connected  A  -fashion  to  the  50,000- volt  line. 

When  transformers  that  will  operate  at  the  desired  line  voltage  on 
A  -connection  can  be  obtained  at  slight  advance  over  the  cost  of  trans- 
formers requiring  Y-connections,  it  is  often  better  practice  to  select  the 
former,  because  this  will  enable  an  increase  of  seventy-three  per  cent  in 
the  voltage  of  transmission  to  be  made  at  any  future  time  by  simply 
changing  to  Y-connections.  Such  an  increase  of  voltage  may  become 
desirable  because  of  growing  loads  or  extension  of  transmission  lines. 

An  example  of  this  sort  came  up  some  time  ago  in  connection  with 
the  transmission  between  Ogden  and  Salt  Lake  City,  which  was  operat- 
ing at  16,000  volts,  three-phase,  with  the  high-pressure  coils  of  transform- 
ers connected  in  A  -form.  By  changing  to  Y-connections  the  line  voltage 
was  raised  seventy-three  per  cent  without  increasing  the  strain  on  trans- 
former insulation. 

In  some  cases  it  is  desirable  to  change  alternating  current  from  two- 
phase  to  three-phase,  or  vice  versa,  for  purposes  of  transmission  or  distri- 
bution, and  this  can  readily  be  done  by  means  of  static  transformers. 
One  method  often  employed  to  effect  this  result  includes  the  use  of  two 
transformers  connected  to  opposite  phases  of  the  two-phase  circuit.  The 
three-phase  coil  of  one  of  these  transformers  should  be  designed  for  the 


TRANSFORMERS  IN  TRANSMISSION  SYSTEMS.     133 

desired  three-phase  voltage,  and  should  have  a  tap  brought  out  from  its 
central  point.  The  three-phase  coil  of  the  other  transformer  should  be 
designed  for  87  per  cent  of  the  desired  three-phase  voltage.  One  end  of 
the  coil  designed  for  87  per  cent  of  the  three-phase  voltage  should  be  con- 
nected to  the  centre  tap  of  the  three-phase  coil  in  the  other  transformer. 
The  other  end  of  the  87  per  cent  coil  goes  to  one  wire  of  the  three-phase 
circuit.  The  other  two  wires  of  this  circuit  should  be  connected,  respect- 
ively, to  the  outside  end  of  the  coil  that  has  the  central  tap.  As  a  matter 
of  illustration  it  may  be  required  to  transform  500- volt,  two-phase  current 
from 'generators,  to  20,000- volt,  three-phase  current  for  transmission. 
Two  transformers  designed  for  500  volts  in  their  primary  coils  are  neces- 
sary for  this  work.  One  of  these  transformers  should  have  a  secondary 
coil  designed  for  20,000  volts,  so  that  the  ratio  of  transformation  is  20,000 
-^  500  or  40  to  i ,  and  a  tap  should  be  brought  out  from  the  centre  of  this 
coil.  The  other  transformer  should  have  a  secondary  voltage  of  0.87  x 
20,000  =  17,400,  so  that  its  ratio  of  transformation  is  34.8  to  i. 

These  two  transformers,  with  the  connections  above  indicated,  will 
change  the  5oo-volt,  two-phase  current  to  20,000  volts,  three-phase. 

At  one  of  the  water-power  stations  supplying  energy  for  use  in  Hart- 
ford, four  transformers  of  300  kilowatts  each  change  5oo-volt,  two- 
phase  current  from  the  generators  to  10,000- volt,  three-phase,  for  the 
transmission  line. 

In  the  Niagara  water-power  station  the  generators  deliver  two-phase 
current  at  2,200  volts,  and  975-kilowatt  transformers  are  connected  in 
pairs  to  change  the  pressure  to  22,000  volts,  three-phase,  for  transmission 
to  Buffalo. 

A  transformer  is  used  in  some  cases  to  raise  the  voltage  and  compen- 
sate for  the  loss  in  a  transmission  line.  For  this  purpose  the  secondary 
of  a  transformer  giving  the  number  of  volts  by  which  the  line  pressure  is 
to  be  increased  is  connected  in  series  with  the  line.  The  primary  wind- 
ing of  this  transformer  may  be  supplied  from  the  line  boosted  or  from 
another  source. 

Transformers  ranging  in  capacity  from  100  to  1,000  kilowatts  each, 
such  as  are  commonly  used  for  transmission  work,  have  efficiencies  of 
96  to  98  per  cent  at  full  loads,  when  of  first-class  construction.  Efficiency 
increases  slowly  with  transformer  capacity  within  the  limits  named,  and 
98  per  cent  can  be  fairly  expected  in  only  the  larger  sizes.  In  any  given 
transformer  the  efficiency  may  be  expected  to  fall  a  little,  say  one  or  two 
per  cent,  between  full  load  and  half  load,  and  another  one  per  cent  be- 
tween half  load  and  quarter  load.  These  figures  for  efficiencies  at  par- 


i34    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


tial  loads  vary  somewhat  with  the  design  and  make  of  transformers.  In 
general,  it  may  be  said  that  step-up  or  step-down  transformers  will  cost 
approximately  #7.50  per  kilowatt  capacity,  or  about  one-half  of  the  like 
cost  of  low-voltage  dynamos.  If  dynamos  of  voltage  sufficiently  high 
for  the  transmission  line  can  be  had  at  a  figure  below  the  combined  cost 
of  low- volt  dynamos  and  raising  transformers,  it  will  usually  pay  to  avoid 
the  latter  and  develop  the  line  voltage  in  the  armature  coils.  This  plan 
avoids  the  loss  in  one  set  of  transformers. 

TRANSFORMERS  IN  TRANSMISSION  SYSTEMS. 


Transformers 

Transformers 

Generators  at 

at   Power- 

at 

Power- 

Transmission  System. 

stations. 

Sub-stations. 

stations. 

No. 

Kw. 
Each. 

No. 

Kw. 

Each. 

No. 

Kw. 

Each. 

Canon  Ferry  to  Butte  

12 

* 

* 

Apple  River  to  St.  Paul  

6 

95° 

6 
6 

95° 

10 

75° 

6 

500 

4 

200 

4 

75° 

White  River  to  Dales  

400 

77C 

2 

COO 

Farmington  River  to  Hartford  

4 

300 

... 

2 

500 
600 

Ogden  to  Salt  Lake  

t9 

250 



.5 

750 

Colgate  to  Oakland  

7 

3 

1125 

' 

U 

2250 

Presumpscot  River  to  Portland.  .  . 

... 

... 

fj 

2OO 

4 

500 

f' 

180 

1  3 

300 

Four  water-powers  to  Manchester. 

... 

... 

21 

2OO 

45° 

4 

650 

LI 

1200 

*  Other  transformers  at  Helena  sub-stations. 

t  Part  of  energy  distributed  directly  from  generators. 


CHAPTER  XI. 

SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS. 

ELECTRICAL  transmission  has  worked  a  revolution  in  the  art  of  switch- 
ing. As  long  as  the  distances  to  be  covered  by  distribution  lines  required 
pressures  of  only  a  few  hundred  volts,  the  switch  contacts  for  generators 
and  feeders  could  well  be  exposed  in  a  row  on  the  surface  of  vertical 
marble  slabs  and  separated  from  each  other  by  distances  of  only  a  few 
inches.  These  switches  were  capable  of  manual  operation  even  at  times 
of  heavy  overload  without  danger  of  personal  injury  to  the  operator  or 
of  destructive  arcing  between  the  parts  of  a  single  switch  or  from  one 
switch  to  another  near-by.  On  the  back  of  these  marble  slabs  one  or 
more  sets  of  bare  bus-bars  could  be  located  without  much  probability 
that  an  accidental  contact  between  them  would  start  an  arc  capable  of 
destroying  the  entire  switchboard  structure  and  shutting  down  the  sta- 
tion. 

The  rise  of  electric  pressures  to  thousands  and  tens  of  thousands  of 
volts  in  distribution  and  transmission  systems  has  vastly  increased  the 
difficulty  of  safe  and  effective  control  with  open-air  switches.  The  higher 
the  voltage  of  the  circuit  to  be  operated  under  load  the  greater  must  be 
the  distance  between  the  contact  parts  of  each  switch  and  also  between 
adjacent  switches.  Such  switches  must  also  be  farther  removed  from 
the  operators  as  the  voltages  of  their  circuits  go  up,  as  a  person  cannot 
safely  stand  very  close  to  an  electric  arc  of  several  feet  or  even  yards  in 
length.  In  the  West,  where  long  transmissions  are  most  common,  long 
break-stick  switches  have  been  much  used  with  high  voltages.  These 
switches  depend  on  the  length  of  the  break  to  open  the  circuit  and  on  the 
length  of  the  stick  that  moves  the  switch-jaw  or  plug  to  insure  the  safety 
of  the  operator.  Where  switches  of  this  sort  are  used  it  is  highly  impor- 
tant to  have  ample  distances  between  the  contact  points  of  each  switch 
and  also  between  the  several  switches.  On  circuits  of  not  more  than 
10,000  volts  an  arc  as  much  as  a  yard  long  will  in  some  cases  follow  the 
opening  switch  blade  and  hold  on  for  several  seconds.  On  the  33,000- 
volt  transmission  line  at  Los  Angeles  a  peculiar  form  of  switch  is  used 


136     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

which  makes  a  break  between  a  pair  of  curved  wire  horns  that  are  ten 
inches  apart  at  their  nearest  points.  When  the  contact  between  these 
horns  is  broken  the  arc  travels  up  between  portions  of  the  horns  that 
curve  apart  and  is  thus  finally  ruptured.  Besides  the  very  large  space 
required  for  open  switches  on  circuits  of  5,000  to  10,000  volts  or  more, 
there  is  a  further  objection  that  the  arcs  developed  by  opening  such 
switches  under  heavy  loads  rapidly  destroy  the  contact  parts  and  produce 
large  quantities  of  metallic  vapor  that  is  objectionable  in  a  central  sta- 
tion. In  some  experiments  performed  at  Kalamazoo  (A.  I.  E.  E.,  vol. 
xviii.,  p.  407)  with  open-air  switches  the  voltages  ranged  from  25,000  to 
40,000.  The  loads  on  circuits  broken  by  the  switches  were  highly  in- 
ductive and  mounted  from  1,200  to  1,300  kilovolt-amperes.  At  25,000 
volts  the  arc  produced  by  the  open-air  switch  held  on  for  several  seconds. 
At  40,000  volts  the  arc  following  the  opening  of  this  switch  was  over 
thirty  feet  long,  and  being  out  of  doors  near  the  pole  line  the  arc  struck 
the  line  wires  and  short-circuited  the  system.  It  has  been  shown  that 
the  oscillations  of  voltage  occurring  when  a  circuit  under  heavy  load  is 
opened  by  an  open-air  switch  may  be  very  dangerous  to  insulation  (A.  I. 
E.  E.,  vol.  xviii.,  p.  383).  In  the  Kalamazoo  test  the  oscillations  of  this 
sort  were  reported  to  have  reached  two  or  three  times  the  normal  voltage 
of  the  system  when  the  open-air  switch  was  used. 

Facts  of  the  nature  just  outlined  have  led  to  the  development  of  oil 
switches.  The  general  characteristic  of  oil  switches  is  that  the  contact 
parts  are  immersed  in,  and  the  break  between  these  contacts  takes  place 
under,  oil.  Two  types  of  the  oil  switch  are  made,  one  having  all  of  its 
contact  parts  in  the  same  bath  of  oil  and  the  other  having  a  separate 
oil-bath  for  each  contact.  Compared  with  those  of  the  open-air  type, 
oil  switches  effect  a  great  saving  of  space,  develop  no  exposed  arcs  or 
metallic  vapors,  cause  little  if  any  oscillation  or  rise  of  voltage  in  an  alter- 
nating circuit,  and  can  be  depended  on  to  open  circuits  of  any  voltage  and 
capacity  now  in  use.  In  the  tests  above  mentioned  at  Kalamazoo,  a 
three-phase  oil  switch  making  two  breaks  in  each  phase  and  with  all  the 
six  contacts  in  a  single  oil-bath  was  used  to  open  circuits  of  25,000  volts 
and  1,200  to  1,300  kilovolt-arcs  with  satisfactory  results.  At  40,000 
volts,  however,  this  type  of  switch  spat  fire  and  emitted  smoke,  indicating 
that  it  was  working  near  its  ultimate  capacity.  A  three-phase  switch 
with  each  of  its  six  contacts  in  a  separate  cylindrical  oil-chamber  was 
used  to  open  the  40,000- volt  i  ,300  kilovolt-arc  circuit  at  Kalamazoo  with 
perfect  success  even  under  conditions  of  short-circuit  and  without  the 
appearance  of  fire  or  smoke  at  the  switch.  The  three-phase  switch  used 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       137 

in  the  tests  at  Kalamazoo  and  having  each  of  its  contacts  in  a  separate 
oil-chamber  was  similar  in  construction  to  the  switches  used  in  the  Metro- 
politan and  Manhattan  railway  stations  in  New  York  City.  In  each  of 
these  switches  the  two  leads  of  each  phase  terminate  in  two  upright  brass 
cylinders.  These  cylinders  have  fibre  linings  to  prevent  side-jumping  of 
the  arcs  when  the  switch  is  opened,  and  each  cylinder  is  filled  with  oil. 
Into  the  two  brass  cylinders  of  each  phase  dips  a  H  -shaped  contact  piece 
through  insulating  bushings,  and  the  ends  of  this  contact  piece  fit  into 
terminals  at  the  bottom  of  the  oil  pots.  A  wooden  rod  joins  the  centre 
or  upper  part  of  the  fl  -contact  piece,  and  the  three  rods  of  a  three-phase 
switch  pass  up  through  the  switch  compartment  to  the  operating  mechan- 
ism outside.  The  six  brass  cylinders  and  their  three  0  -contact  pieces 
are  usually  mounted  on  a  switch  cell  built  entirely  of  brickwork  and 
stone  slabs.  For  a  three-phase  switch  the  brick  and  stone  cell  has  three 


Feeders  Feeders 

>  POWER  HOUSE      } 

No2 

.  ,    I  Bus,.    Bars,    1          |*|  nBu.|*UJ    ^ 

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j'          I  i      Bus  jl    Bars  |  I  J  >{     Bus  J    Bars  t  j          j    i 

i  6  o  o  6  6      6  ©  6  o  oiM 


Gensrators                                                                    Gene/ators  t>| 

i?  Ml    j 

j  §                           Generators                                                                    Generators  g!    I 

!l  Q  Q  (5  G)  Q        9  9  G> '  9  9  f!  i 

I   -    .  b        t  .  I   Bu?  .  I    Ba.fS  I                —  >-                ,1        .  ,1     Bus!    Bars   I  ,1      f"l    ! 

-    r  *r.l  M.  '*T.  i^.  J/'MV""     **i  I1*!  UM.  ll*i  I1*'     J 


M    Bus  U  Bars  Lr  W          IvfBus 

POWERHOUSE 

¥«•» 

Feeders  Feeders 


IrfBt^f 

I 


FIG.  55.— Connections  between  Power-houses  i  and  2  at  Niagara  Falls. 

entirely  separate  compartments,  and  each  compartment  contains  the  two 
brass  cylinders  that  form  the  terminals  of  a  single  phase.  On  top  of  and 
outside  the  cell  the  mechanism  for  moving  the  wooden  switch  rods  is 
mounted.  In  the  Metropolitan  station,  where  the  voltage  is  6,000,  the 
vertical  movement  of  the  fl  -shaped  contact  piece  with  its  rod  is  twelve 
inches.  At  the  Manhattan  station,  where  the  operating  voltage  is  1 2,000, 
the  vertical  movement  of  the  f| -con tacts  in  opening  a  switch  is  seventeen 
inches.  The  total  break  in  each  phase  in  a  switch  at  the  Metropolitan 
station  is  thus  twenty-four  inches,  or  four  inches  per  i  ,000  volts,  and  the 


138     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

total  break  per  phase  in  switches  at  the  Manhattan  station  is  thirty-four 
inches,  or  2.66  inches  per  1,000  volts  total  pressure. 

Oil  switches  are  now  very  generally  employed  on  alternating  circuits 
that  operate  at  2,000  volts  or  more  for  purposes  of  general  distribu- 
tion. On  circuits  of  moderate  voltage  like  that  just  named,  and  even 
higher,  it  is  common  practice  to  use  oil  switches  that  have  only  a  single 
reservoir  of  oil  each,  the  entire  six  contacts  in  the  case  of  a  three-phase 
switch  being  immersed  in  this  single  reservoir.  Such  switches  are  usu- 
ally operated  directly  by  hand  and  are  located  on  the  backs  of  or  close 
to  the  slate  or  marble  boards  on  which  the  handles  that  actuate  the  switch 
mechanism  are  located.  A  good  example  of  this  sort  of  work  may  be 
seeC  at  the  sub-station  in  Manchester,  N.  H.,  where  energy  from  four 
water-power  stations  is  delivered  over  seven  transmission  lines  and  then 
distributed  by  an  even  larger  number  of  local  circuits  at  2,000  volts  three- 
phase.  At  the  Garvin's  Falls  station,  one  of  the  water-power  plants  that 
delivers  energy  to  the  sub-station  in  Manchester,  the  generators  operate 
at  1 2,000  volts  three-phase,  and  these  generators  connect  directly  with 
the  bus-bars  through  hand-operated  oil  switches  on  the  back  of  the 
marble  switchboard.  These  last-named  switches,  like  those  at  the 
Manchester  sub-station,  have  all  the  contacts  of  each  in  a  single  res- 
ervoir of  oil. 

With  very  high  voltages,  where  only  a  few  hundred  kilowatts  are  con- 
cerned, and  also  with  powers  running  into  thousands  of  kilowatts  at 
as  low  a  pressure  as  2,000  volts,  it  is  very  desirable  to  remove  even  oil 
switches  from  the  switchboard  and  the  vicinity  of  the  bus-bars.  Great 
powers  as  well  as  very  high  voltages  not  only  increase  the  element  of 
personal  danger  to  an  attendant  who  must  stand  close  to  a  switch 
while  operating  it,  but  also  render  the  damage  to  other  apparatus  that 
may  result  from  any  failure  of  or  short-circuit  in  a  switch  much  more 
serious. 

As  soon  as  the  switches  are  removed  to  a  distance  from  the  operating 
board  the  necessity  for  some  method  of  power  control  becomes  evident, 
since  the  operator  at  the  switchboard  should  be  able  to  make  or  break 
connections  of  any  part  of  the  apparatus  quickly.  The  necessity  for  the 
removal  of  switches  for  very  large  powers  to  a  distance  from  the  operating 
boards  and  for  the  application  of  mechanical  power  to  make  and  break 
connections  was  met  before  the  development  of  oil  switches.  Thus  at 
the  first  Niagara  (A.  I.  E.  E.,  vol.  xviii.,  p.  489)  power-house,  in  1893, 
the  switches  for  the  3,750-kilowatt,  2,2oo-volt  generators,  though  of  the 
open-air  type,  were  located  in  a  special  switch  compartment  erected  in 


SWITCHES,  FUSES,  AND  CIRCUIT -BREAKERS.       139 


FIG.  56—  Wire-room  Back  of  Switchboard  in  Power-station  on  French  Broad  River,  North  Carolina. 


140    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  generator  room  and  over  a  cable  subway  at  some  distance  from  the 
operating  board.  These  switches  were  actuated  through  compressed-air 
cylinders  into  which  air  was  admitted  by  the  movement  of  levers  near 
the  switchboard.  Evidently  a  switch  of  this  capacity — i  ,000  amperes  per 
pole  and  2,200  volts,  two-phase — could  not  well  be  operated  by  hand- 
power  wherever  located,  because  of  the  large  effort  required.  In  the 
second  generating  station  at  Niagara  Falls  oil  switches  similar  to  those 


FIG.  57.— Section  through  Cable  Subway  under  Oil  Switches  in  Niagara 
Power-house  No.  2. 


used  at  the  Manhattan  Elevated  Railway  plant  in  New  York,  but  two- 
phase,  were  employed.  Each  of  these  oil  switches  at  Niagara  Falls  has 
a  capacity  of  5,000  horse-power,  like  the  previous  open-air  switches, 
and  is  electrically  actuated. 

In  these  electrically  operated  oil  switches  a  small  motor  is  located  on 
top  of  the  brick  cell  that  contains  the  contact  parts,  and  this  motor  re- 
leases and  compresses  springs  that  open  and  close  the  switch.  While  it 
is  not  desirable  to  employ  open-air  switches  to  open  circuits  of  several 
thousand  or  even  hundreds  of  kilowatts  at  voltages  of  2,000  or  more,  it 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       141 

is  nevertheless  possible  to  do  so.  This  is  shown  by  the  experience  of  the 
first  Niagara  Falls  station,  where  the  2, 200- volt  two-phase  switches  are 
reported  to  have  opened  repeatedly  currents  of  more  than  600  amperes 
per  phase  without  injurious  sparking.  The  great  rise  of  voltage  that  was 
shown  by  the  experiments  at  Kalamazoo  to  follow  the  opening  of  a  simple 
open-air  switch  was  avoided  at  the  first  Niagara  switches  by  a  simple 
expedient.  In  these  5,000  horse-power  open-air  switches  a  shunt  of  high 
resistance  was  so  connected  between  each  pair  of  contacts  that  the  blades 


FIG.  58.    Schenectady  Switch-house  on  Spier  Falls  Line. 


and  jaws  that  carried  the  main  body  of  the  current  never  completely 
opened  the  circuit.  When  the  main  jaws  of  one  of  these  switches  were 
opened  the  shunt  resistance  continued  in  circuit  until  subsequently 
broken  at  auxiliary  terminals.  That  no  excessive  rise  of  voltage  took 
place  when  one  of  these  switches  was  open  was  shown  by  connecting  two 
sharp  terminals  in  parallel  with  the  switch  and  by  adjusting  these  termi- 
nals to  a  certain  distance  apart.  Had  the  voltage  risen  on  opening 
the  switch  above  the  predetermined  amount  there  would  have  been 
an  arc  formed  by  a  spark  jumping  the  distance  between  the  pointed 
terminals. 


142     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Safety  and  reliability  of  operation  at  high  voltages,  say  of  5,000  or 
more,  require  that  each  element  of  the  equipment  be  so  isolated  as  well 
as  insulated  from  every  other  element  that  the  failure  or  even  destruction 
of  one  element  will  not  seriously  endanger  the  others.  With  this  end  in 
view  the  cables  from  each  generator  to  its  switch  should  be  laid  in  a  con- 
duit of  brick  or  concrete  that  contains  no  other  cables.  The  brick  or 


FIG.  59.— Second-floor  Plan  of  Saratoga  Switch-house  on  Spier  Falls  Line. 


stone  compartment  for  each  phase  of  each  switch  should  be  so  substantial 
that  the  contacts  of  that  phase  may  arc  to  destruction  without  injury  to 
the  contacts  of  another  phase.  Bus-bars,  like  switches,  should  be  re- 
moved from  the  operating  switchboard,  because  an  arc  between  them 
might  destroy  other  apparatus  thereon,  and  even  the  board  itself.  It  is 
not  enough  to  remove  bus-bars  from  the  switchboard  where  very  high 
voltages  are  to  be  controlled,  but  each  bar  should  be  located  in  a  separate 
brick  compartment  so  that  an  arc  cannot  be  started  by  accidental  contact 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       143 

between  two  or  more  of  the  bars.  It  is  convenient  to  have  the  brick  and 
stone  compartments  for  bus-bars  built  horizontally  one  above  the  other. 
The  top  and  bottom  of  each  compartment  may  conveniently  be  formed 
of  stone  slabs  with  brick  piers  on  one  side  and  a  continuous  brick  wall 
on  the  other  to  hold  the  stone  slabs  in  position.  Connections  to  the 
bus-bars  should  pass  through  the  continuous  brick  wall  that  forms 
what  may  be  termed  the  back  of  the  compartments.  To  close  the  open- 


FlG.  60.— Ground  Floor  of  Saratoga  Switch-house. 


ings  between  the  brick  piers  at  the  front  of  the  compartments  movable 
slabs  of  stone  may  be  used.  Feeders  passing  away  from  the  bus-bars, 
like  dynamo  cables  running  to  these  bars,  should  not  be  grouped  close 
together  in  a  single  compartment,  but  each  cable  or  circuit  should  be 
laid  in  a  separate  fireproof  conduit  to  the  point  where  it  passes  out  of 
the  station. 

The  folly  of  grouping  a  large  number  of  feeders  that  transmit  great 
powers  together  in  a  single  combustible  compartment  was  well  illus- 
trated by  the  accident  that  destroyed  the  cables  that  connected  the  first 
Niagara  power-station  with  the  transformer-house  on  January  29th, 


144     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

1903.  On  the  evening  of  that  day  lightning  short-circuited  one  of  the 
cables  in  the  short  bridge  that  connects  No.  i  station  with  the  trans- 
former-house, and  all  the  cables  in  this  bridge,  supplying  local  consumers 
as  well  as  railways  and  lighting  in  Buffalo,  were  destroyed.  This  bridge 
contained  probably  more  than  thirty-six  cables,  as  that  number  of  new 
cables  was  put  in  position  within  twenty-four  hours  after  the  accident, 
and  these  cables,  covered  with  inflammable  insulation,  were  close 
together.  The  result  was  not  only  the  loss  of  the  cables,  but  also  the 
damage  to  power  users.  If  these  cables  had  been  located  in  separate 
fire-proof  conduits,  it  is  highly  probable  that  only  the  one  directly 
affected  by  lightning  would  have  been  destroyed. 

The  brick  and  stone  compartments  for  bus-bars  may  be  located  in 
the  basement  underneath  the  switchboard,  as  at  the  Portsmouth  station 
of  the  New  Hampshire  Traction  Company,  or  at  any  other  place  in  a 
station  where  they  are  sufficiently  removed  from  the  other  apparatus. 
In  power-house  No.  2  at  Niagara  Falls  a  cable  subway  beneath  the  floor 
level  runs  the  entire  length,  parallel  with  the  row  of  generators  (A.  I.  E. 
E.,  vol.  xix.,  p.  537).  In  this  subway,  which  is  thirteen  feet  nine  and 
three-quarter  inches  wide  and  ten  feet  six  inches  high,  the  two  structures 
for  bus-bar  compartments  are  located.  Each  of  these  structures  meas- 
ures about  6.6  feet  high  and  1.8  feet  wide,  and  contains  four  bus-bar 
compartments.  In  each  compartment  is  a  single  bar,  and  the  four  bars 
form  two  sets  for  two-phase  working.  Above  the  bus-bar  compartments 
and  rising  from  the  floor  level  are  the  oil  switches.  A  space  over  the 
cable  subway  midway  of  its  length  and  between  the  two  groups  of  oil 
switches  is  occupied  by  the  switchboard  gallery  which  is  raised  to  some 
elevation  above  the  floor  and  carries  eleven  generator,  twenty-two  feeder, 
two  interconnecting,  and  one  exciter  panels.  In  power-house  No.  i  the 
bus-bars  are  located  in  a  common  space  above  the  5,000  horse-power 
open-air  switches  already  mentioned,  and  each  bar  has  an  insulation  of 
vulcanized  rubber  covered  with  braid  and  outside  of  this  a  wrapping  of 
twine.  Of  course;  an  insulation  of  this  sort  would  amount  to  nothing  if 
by  any  accident  an  arc  were  started  between  the  bars.  Where  each  bus- 
bar is  located  in  a  separate  fireproof  compartment,  as  at  Niagara  power- 
house No.  2,  the  application  of  insulation  directly  to  each  bar  is  neither 
necessary  nor  desirable.  Consequently  the  general  practice  where  each 
bar  has  its  own  fireproof  compartment  is  to  construct  the  bars  of  bare 
copper  rods. 

With  main  switches  for  generators  and  feeders  removed  from  the 
operating  board  and  actuated  by  electric  motors  or  magnets,  the  small 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       145 

switches  at  the  board  with  which  the  operator  is  directly  concerned  must 
of  course  control  these  magnets  or  motors.  The  small  switches  at  the 
operating  board  are  called  relay  switches,  and  the  current  in  the  cir- 
cuits opened  and  closed  by  these  switches  and  used  to  operate  the  mag- 
nets or  motors  of  the  oil  switches  may  be  conveniently  obtained  from  a 
storage  battery  or  from  one  of  the  exciting  dynamos. 

Probably  the  best  arrangement  of  the  relay  switches  is  in  connection 
with  dummy  bus-bars  on  the  face  of  the  switchboard,  so  that  the  connec- 
tions on  the  face  of  the  board  constitute  at  all  times  a  diagram  of  the 
actual  connections  of  the  generator  and  feeder  circuits.  It  is  also  desira- 
ble for  quick  and  correct  changes  in  the  connections  of  the  main  appa- 
ratus that  all  the  relay  switches  and  instruments  necessary  for  the  control 
of  any  one  generator  or  any  one  feeder  be  brought  together  on  a  single 
panel  of  the  switchboard.  If  this  plan  is  followed,  the  operator  at  any 
time  will  have  before  him  on  a  single  panel  all  of  the  switches  and  instru- 
ments involved  in  the  connections  then  to  be  made,  and  the  chance  for 
mistakes  is  thus  reduced  to  a  minimum.  The  plan  just  outlined  was 
that,  adopted  at  the  Niagara  power  plant  No.  2,  where  a  separate  panel 
is  provided  for  each  of  eleven  generators  and  each  of  twenty-two  feeders. 
On  each  of  the  eleven  generator  panels  there  are  two  selector  relay 
switches,  one  generator  relay  switch,  and  one  relay  generator  field  switch. 
On  each  of  the  twenty-two  feeder  panels  there  are  two  relay  selector 
switches.  The  relay  switches  on  the  two  interconnecting  panels  serve 
to  make  connections  between  the  two  groups  of  five  and  six  generators 
respectively  in  power-house  No.  2  and  the  ten  generators  of  power-house 
No.  i .  On  each  panel  there  are  relay  indicators  to  show  whether  the  oil 
switches  that  carry  the  main  current  respond  to  the  movements  of  their 
relay  switches. 

Where  the  electric  generators  operate  at  the  maximum  voltage  of  the 
system,  as  at  Garvin's  Falls  and  in  the  power-house  of  the  Manhattan 
Elevated  Railway,  there  may  be  said  to  be  only  one  general  plan  of  con- 
nections possible.  That  is,  the  generators  must  connect  directly  with 
the  main  bus-bars  at  the  voltage  of  the  system,  and  the  feeders  or  trans- 
mission lines  must  also  connect  to  these  same  bars.  Of  course  there 
may  be  several  sets  of  bus-bars  for  different  circuits  or  classes  of  work, 
but  this  does  not  change  the  general  plan  of  through  connections  from 
generators  to  lines.  So,  too,  the  arrangement  of  switches  is  subject 
to  variations,  as  by  placing  two  switches  in  series  with  each  other  in 
each  dynamo  or  feeder  cable,  or  by  connecting  a  group  of  feeders 
through  their  several  switches  to  a  particular  set  of  bus-bars  and  then 
10 


146    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

supplying  this  set  of  bars  from  the  generator  bus-bars  through  a  single 
switch. 

Where  the  voltage  of  transmission  is  obtained  by  the  use  of  step-up 
transformers,  the  connections  of  these  transformers  may  be  such  as  to 


Transformer"^ 


n  n  n 

LO^  *•+     ^,1  k/     ly  U^ 


FIG.  61.— Switchboard  Wiring,  Glens  Falls  Sub-station  on  Spier  Falls  Line. 


require  nearly  all  switching  to  be  done  on  either  the  high-  or  low-tension 
circuits.  The  more  general  practice  was  formerly  to  do  all  switching  in  the 
generator  circuits  and  on  the  low-tension  side  of  transformers,  except  in 
the  connection  and  disconnection  of  transformers  and  transmission  lines 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.      147 

with  the  high-tension  bus-bars,  when  not  in  operation.  Where  generators 
operate  at  the  maximum  voltage  of  the  system  only  two  main  groups  of 
switches  are  necessary,  one  group  connecting  generators  to  bus-bars,  and 
the  other  group  connecting  bus-bars  to  the  transmission  lines.  As  soon 
as  step-up  transformers  are  introduced  the  number  of  switch  groups 
must  be  increased  to  four  if  the  usual  method  of  connection  is  followed, 
and  there  must  be  both  a  high  voltage  and  a  low  voltage  set  of  bus-bars. 
That  is,  one  set  of  switches  must  connect  generators  with  low-tension 
bus-bars,  another  group  must  connect  low-tension  bars  with  the  primary 
coils  of  transformers,  a  third  group  joins  the  secondary  coils  of  transform- 
ers with  the  high-tension  bars,  and  the  fourth  group  of  switches  joins  the 
transmission  lines  to  the  high-tension  bus-bars.  Switches  connecting 
the  secondary  coils  of  step-up  transformers  to  the  high-tension  bus- 
bars, and  also  the  transmission  lines  to  these  same  bars,  have  often 
been  of  the  simple  open-air  type  with  short  knife-blade  construction. 
These  switches  have  been  used  to  disconnect  the  secondary  coils  of 
transformers  and  also  the  transmission  lines  from  the  high-tension  bus- 
bars when  no  current  was  flowing,  and  switches  of  the  simple  knife- 
blade  construction  with  short  breaks  could  of  course  be  used  for  no 
other  purpose.  With  switches  of  this  sort  on  the  high-tension  side  of 
apparatus  the  practice  is  to  do  all  switching  of  line  circuits  on  the  low- 
tension  side. 

It  is  possible  to  avoid  some  of  this  multiplication  of  switches  if 
each  generator  with  its  transformers  is  treated  for  switching  purposes 
as  a  unit  and  the  switching  for  this  unit  is  done  on  the  secondary  or 
high-voltage  side  of  the  step-up  transformers.  The  adoption  of  this 
plan,  of  course,  implies  the  use  of  switches  that  are  competent  to  break 
the  secondary  circuit  of  any  group  of  transformers  under  overload 
conditions  and  at  the  maximum  voltage  of  the  system,  but  oil  switches 
as  now  made  are  competent  to  meet  this  requirement.  When  all 
switching  of  live  circuits  is  confined  to  those  of  high  voltage  there  is 
also  the  incidental  advantage  that  heavy  contact  parts  carrying  very 
large  currents  are  avoided  in  the  operating  switches.  Where  each  gen- 
erator is  connected  directly  to  its  own  group  of  transformers  the  secon- 
dary coils  of  these  transformers  will  pass  through  oil  switches  to  high- 
tension  bus-bars,  and  the  use  of  low-tension  bus-bars  may  be  avoided. 
From  these  high-tension  bus-bars  the  transmission  lines  will  pass  through 
oil  switches,  so  that  on  this  plan  there  are  only  two  sets  of  oil  switches, 
namely,  those  connecting  the  secondary  coils  of  transformers  to  the  high- 
tension  bus-bars,  and  those  connecting  the  transmission  lines  to  the  same 


i48    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

bars.  Each  group  of  two  or  three  transformers,  according  as  two  or 
three  are  used  with  each  generator,  should  be  connected  to  its  generator 
through  short-break,  open-air  knife  switches  for  convenienec  in  discon- 
necting and  changing  transformers  that  are  not  in  operation,  but  these 


switches  are  not  intended  or  required  to  open  the  circuit  of  the  generators 
and  primary  coils  when  in  operation. 

A  plan  similar  to  that  just  outlined  was  followed  at  the  station  of  the 
Independent  Electric  Light  and  Power  Company,  San  Francisco,  where 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       149 

each  of  the  5  50- volt  generators  is  ordinarily  connected  directly  to  the 
primary  coils  of  two  transformers  that  change  the  current  from  two-phase 
to  three-phase  and  then  deliver  it  through  oil  switches  to  the  high-tension 
bus-bars  at  11,000  volts.  To  these  bus-bars  the  n,ooo-volt  feeders  for 
five  sub-stations  are  connected  through  switches.  At  this  station  there 
is  a  set  of  5  50- volt  bus-bars  to  which  any  of  the  generators  may  be  con- 
nected, but  to  which  no  generator  is  connected  in  ordinary  operation. 
The  generators  alone  have  switches  connecting  with  these  bars.  When 
it  is  desirable  to  operate  any  particular  generator  on  some  pair  of  trans- 


FlG.  63. — Switchboard  at  Chambly  Power-station. 

formers  other  than  its  own,  that  generator  is  disconnected  from  its  own 
transformers  and  connected  to  the  5 50- volt  bus-bars.  The  generator 
whose  transformers  are  to  be  operated  by  the  generator  before  mentioned 
next  has  its  switch  connected  to  the  5  50- volt  bus-bars,  while  the  brushes 
of  the  contact  rings  of  the  former  generator  are  raised.  As  the  leads 
from  each  generator  to  its  two  switches  are  permanently  joined,  the 
switching  operations  just  named  connect  the  transformers  of  one 
generator  with  the  other  generator  that  has  its  switch  closed  on  the 
5  50- volt  bars. 

Where  it  is  desired  that  a  single  reserve  transformer  may  be  readily 
substituted  for  any  one  of  a  number  of  transformers  in  regular  use,  the 
connections  to  each  of  these  latter  transformers  may  be  provided  with 


150    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

double-pole  double-throw  knife  switches  on  both  the  primary  and  sec- 
ondary sides,  so  that  when  these  switches  are  thrown  one  way  at  any 
transformer  in  regular  use  the  reserve  transformer  will  be  connected  in 
its  place. 

Fuses  and  automatic  circuit-breakers  alike  are  intended  to  break  con- 
nections without  the  intervention  of  human  agency  under  certain  prede- 
termined conditions.  In  the  fuse  the  heat  generated  by  a  certain  cur- 
rent is  sufficient  to  melt  or  vaporize  a  short  length  of  special  conductor. 
In  the  circuit-breaker  a  certain  current  gives  a  magnet  or  motor  sufficient 
strength  to  overcome  the  pressure  of  a  spring,  and  contact  pieces  through 
which  the  current  is  passing  are  pulled  apart.  The  primary  object  of 
both  the  fuse  and  the  circuit-breaker  is  thus  to  open  connections  and 
stop  the  flow  of  energy  when  more  than  a  certain  current  passes.  When 
any  current  passes  through  a  circuit  in  the  reverse  of  its  regular  direction 
the  circuit-breaker  can  be  arranged  to  break  the  connections,  though  the 
fuse  cannot.  A  fuse  must  carry  the  current  at  which  it  is  designed  to 
melt  during  some  seconds  before  enough  heat  is  developed  to  destroy  it, 
and  the  exact  number  of  seconds  for  any  particular  case  is  made  a  little 
uncertain  by  the  possibility  of  loose  connections  at  the  fuse  tips  which 
develop  additional  heat  and  also  by  the  heat-conducting  power  of  its  con- 
necting terminals.  A  circuit-breaker  may  be  set  so  as  to  open  its  connec- 
tions in  one  or  more  seconds  after  a  certain  current  begins  to  flow. 
When  connections  are  broken  by  a  fuse  the  molten  or  vaporized  metal 
forms  a  path  that  an  arc  may  easily  follow.  A  circuit-breaker  with  its 
contacts  under  oil  offers  a  much  smaller  opportunity  than  a  fuse  for  the 
maintenance  of  an  arc.  These  qualities  of  fuses  and  circuit-breakers 
form  the  basis  of  their  general  availability  and  comparative  advantages 
in  transmission  circuits. 

Much  variation  exists  in  practice  as  to  the  use  of  fuses  and  circuit- 
breakers  on  transmission  circuits.  One  view  often  followed  is  that  fuses 
and  circuit-breakers  should  be  entirely  omitted  from  the  generator  and 
transmission  lines.  The  argument  in  favor  of  this  practice  is  that  tem- 
porary short  circuits  due  to  birds  that  fly  against  the  lines  or  to  sticks  and 
loose  wires  that  are  thrown  onto  them  will  interrupt  all  or  a  large  part  of 
the  transmission  service  if  fuses  or  circuit-breakers  that  operate  instantly 
are  employed.  On  the  other  hand,  it  may  be  said  that  if  fuses  and  cir- 
cuit-breakers are  omitted  from  the  generator  and  transmission  circuits 
a  lasting  short  circuit  will  make  it  necessary  to  shut  down  an  entire  plant 
in  some  cases  until  it  can  be  removed.  Electric  transmission  at  high 
voltages  became  important  before  magnetic  circuit-breakers  competent 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.       151 

to  open  overloaded  circuits  at  such  voltages  were  developed.  Conse- 
quently the  early  question  was  whether  a  transmission  line  and  the  gen- 
erators that  fed  it  should  be  provided  with  fuses  or  be  solidly  connected 
from  generators  to  the  distribution  circuits  of  sub-stations.  The  original 
tendency  was  strong  to  use  fuses  in  accord  with  the  practice  at  low  volt- 
ages. The  great  importance  of  continuous  service  from  transmission 
systems  and  the  many  interruptions  caused  by  temporary  short  circuits 
where  fuses  were  used  led  to  their  abandonment  in  some  cases.  An 
example  of  this  sort  may  be  seen  at  the  first  Niagara  station.  In  1893, 
when  this  station  was  equipped,  no  magnetic  circuit-breaker  was  availa- 
ble for  circuits  of  either  11,000  or  2,200  volts,  carrying  currents  of  several 
thousand  horse-power,  and  fuses  were  employed  in  lines  at  both  these 
pressures  (A.  I.  E.  E.,  vol.  xviii.,  pp.  495, 497).  The  fuses  adopted  in  this 
case  were  the  same  for  both  the  2,200  and  the  n,ooo-volt  lines  and  were 
of  the  explosive  type.  Each  complete  fuse  consisted  of  two  lignum- vitae 
blocks  that  were  hinged  together  at  one  end  and  were  secured  when 
closed  at  the  other.  In  these  blocks  three  parallel  grooves  for  fuses  were 
cut  and  in  each 'groove  a  strip  of  aluminum  was  laid  and  connected  to 
suitable  terminals  at  each  end.  Vents  were  provided  for  the  grooves  in 
which  the  aluminum  strips  were  placed  so  that  the  expanding  gas  when 
a  fuse  was  blown  would  escape.  When  these  fuse  blocks  were  new  and 
the  blocks  of  lignum  vitae  made  tight  joints  the  metallic  vapor  produced 
when  a  fuse  was  blown  was  forced  out  at  the  vents  and  the  connections  of 
the  line  were  thus  broken.  After  a  time,  however,  when  the  joints  between 
the  blocks  were  no  longer  tight  because  of  shrinkage,  the  expanding  gas 
of  the  fuse  would  reach  the  terminals  and  an  arc  would  continue  after 
the  fuse  had  blown.  These  aluminum  fuses,  which  were  adopted  about 
1 893 ,  were  abandoned  at  the  Niagara  plant  in  1 898.  Since  this  later  date 
the  2, 200- volt  feeders  from  the  No.  i  power-house  to  the  local  consumers 
have  had  no  fuses  at  the  power-house,  nor  have  circuit-breakers  been 
installed  there  in  the  place  of  the  fuses  that  were  removed.  At  tKe  large 
manufacturing  plants  supplied  through  these  local  Niagara  feeders,  the 
feeders  formerly  terminated  in  fuses,  but  these  have  since  been  displaced 
by  circuit-breakers.  In  the  second  Niagara  power-station,  completed  in 
1902,  the  local  2, 200- volt  feeders  are  provided  with  circuit-breakers,  but 
no  fuses.  Between  the  generators  and  bus-bars  of  the  first  Niagara  plant 
the  circuits  were  provided  with  neither  fuses  nor  automatic  circuit-break- 
ers, and  this  practice  continues  there  to  the  present  time. 

Besides  the  aluminum  fuses  in  the  n,ooo-volt  transmission  line  at 
the  first  Niagara  station,  there  were  lead  fuses  in  the  2, 200- volt  primary 


152     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

circuits  of  the  step-up  transformers  that  supplied  these  lines.  At  the 
other  end  of  these  lines,  in  the  Buffalo  sub-station,  another  set  of  alumi- 
num fuses  was  inserted  before  connection  was  made  with  the  step-down 
transformers.  Between  the  secondary  coils  of  these  transformers  and 
the  5  50- volt  converters  there  were  no  fuses,  but  these  converters  were  con- 
nected to  the  railway  bus-bars  through  direct  current  circuit-breakers. 
These  lead  fuses,  which  contained  much  more  metal  than  those  of  alu- 
minum, when  blown  set  up  arcs  that  lasted  until  power  was  cut  off  by 
opening  a  switch,  and  usually  destroyed  their  terminals.  An  effort  was 
made  to  so  adjust  the  sizes  of  the  fuses  in  this  transmission  system  that 
in  case  of  a  short  circuit  in  distribution  lines  at  Buffalo  only  the  fuses  in 
the  sub-station  would  be  blown,  leaving  those  at  Niagara  entire.  This 
plan  did  not  prove  effective,  however,  and  a  severe  overload  on  the  distri- 
bution lines  in  Buffalo  would  blow  out  fuses  clear  back  to  the  generator 
bus-bars  at  the  Niagara  station. 

In  order  to  accomplish  the  opening  of  overloaded  circuits  with  greater 
certainty,  to  delay  such  opening  where  the  overload  might  be  of  only  a 
momentary  nature,  and  to  confine  the  open  circuit  to  the  lines  where  the 
overload  existed,  automatic  circuit-breakers  were  substituted  for  the  fuses 
named  in  the  Niagara  and  Buffalo  transmission  system.  This  system 
was  also  changed  from  11,000  to  22,000  volts  on  the  transmission  lines, 
thus  rendering  the  requirements  as  to  circuit-opening  devices  more  se- 
vere. These  circuit-breakers  were  fitted  with  time-limit  attachments  so 
that  any  breaker  could  be  set  to  open  at  the  end  of  any  number  of  seconds 
after  the  current  flowing  through  it  reached  a  certain  amount.  A  circuit- 
breaker  with  such  a  time-limit  attachment  will  not  open  until  the  time 
for  which  it  is  set,  after  the  amperes  flowing  through  it  reach  a  certain 
figure,  has  elapsed,  no  matter  how  great  the  current  may  be.  Moreover, 
if  the  overload  is  removed  from  a  line  before  the  number  of  seconds  for 
which  its  time-limit  circuit-breaker  is  set  have  elapsed,  the  circuit-breaker 
resets  itself  automatically  and  does  not  open  the  connections.  If  a  cir- 
cuit-breaker is  set  to  open  a  line  after  an  interval  of  say  three  seconds 
from  the  time  when  its  current  reaches  the  limit,  the  line  will  not  be 
opened  by  a  mere  momentary  overload  such  as  would  blow  out  a  fuse. 
By  setting  the  time-limit  relays  of  circuit-breakers  in  transmission  lines 
to  actuate  the  opening  mechanism  after  three  seconds  from  the  time  that 
an  overload  comes  on,  and  then  leaving  the  breakers  on  distribution  lines 
to  operate  without  a  time-limit,  it  seems  that  the  opening  of  breakers  on 
the  distribution  lines  should  free  the  system  from  an  overload  there  before 
the  breakers  on  the  transmission  lines  have  time  to  act.  Such  a  result 


SWITCHES,  FUSES,  AND  CIRCUIT-BREAKERS.      153 

is  very  desirable  in  order  that  the  entire  service  of  a  transmission  system 
may  not  be  interrupted  every  time  there  is  a  fault  or  short  circuit  on  one 
of  its  distribution  lines.  This  plan  was  followed  in  the  Niagara  and 
Buffalo  system.  In  the  2 2,000- volt  lines  at  the  Niagara  station  the  time 
relays  were  set  to  actuate  the  breakers  after  three  seconds,  at  the  terminal 
house  in  Buffalo,  where  the  transformers  step  down  from  22,000  to 
1 1 ,000  volts,  the  circuit-breakers  in  the  1 1 ,000  volt  lines  to  sub-stations 
had  their  relays  set  to  open  in  one  second.  Finally  the  circuit-breakers 
in  the  distribution  lines  from  the  several  sub-stations  were  left  to  operate 
without  any  time  limit.  By  these  means  it  was  expected  that  a  short 
circuit  in  one  of  the  distribution  circuits  from  a  sub-station  would  not 
cause  the  connections  of  the  underground  cable  between  that  sub-station 
and  the  terminal  house  to  be  broken,  because  of  the  instant  action  of  the 
circuit-breaker  at  the  sub-station.  Furthermore,  it  was  expected  that  a 
short  circuit  in  one  of  the  underground  cables  between  the  terminal  house 
and  a  sub-station  would  be  disconnected  from  the  transmission  line  at 
that  house  and  would  not  cause  the  circuit-breakers  at  the  Niagara  sta- 
tion to  operate.  It  is  reported  that  the  foregoing  arrangement  of  circuit- 
breakers  with  time  relays  failed  of  its  object  because  the  breakers  did  not 
clear  their  circuits  quick  enough  and  that  the  time-limit  attachments  on 
the  22,000  and  11,000  volt  lines  are  no  longer  in  use  (A.  I.  E.  E.,  vol. 
xviii.,  p.  500).  As  the  circuits  under  consideration  convey  thousands  of 
horse-power  at  11,000  and  22,000  volts  it  may  be  that  time-limit  de- 
vices with  circuit-breakers  would  give  good  results  under  less  exacting 
conditions.  Time-limit  relays  are  perhaps  an  important  aid  toward  relia- 
ble operation  of  transmission  systems,  but  they  are  subject  to  the  objec- 
tion that  no  matter  how  great  the  overload  they  will  not  open  the  circuit 
until  the  time  for  which  they  are  set  has  run.  In  the  case  of  a  short  circuit 
the  time-limit  relay  may  lead  to  a  prolonged  drop  in  voltage  throughout 
the  system,  which  is  very  undesirable  for  the  lighting  service  and  also 
allows  all  synchronous  apparatus  to  fall  out  of  step.  With  a  mere  momen- 
tary drop  in  voltage  the  inertia  of  the  rotating  parts  of  synchronous  ap- 
paratus will  keep  them  in  step.  For  these  reasons  it  is  desirable  to  have 
circuit-breakers  that  will  act  immediately  to  open  a  line  on  which  there  is 
a  short  circuit  or  very  great  overload,  but  will  open  the  line  only  after  an 
interval  of  one  or  more  seconds  when  the  overload  is  not  of  a  very  extreme 
nature.  This  action  on  the  part  of  circuit-breakers  at  the  second  Niagara 
power-station  was  obtained  by  the  attachment  of  a  dash-pot  to  the  trip- 
ping plunger  of  each  circuit-breaker  (A.  I.  E.  E.,  vol.  xviii.,  p.  543).  With 
moderate  overloads  of  a  very  temporary  nature  this  dash-pot  so  retards 


154    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  action  of  a  tripping  plunger  that  the  circuit-breaker  does  not  open. 
When  a  short  circuit  or  great  overload  comes  onto  a  line  the  pull  on  the 
tripping  plunger  or  the  circuit-breaker  on  that  line  is  so  great  that  the 
resistance  of  the  dash-pot  to  the  movement  is  overcome  at  once  and  the 
line  is  disconnected  from  the  remainder  of  the  system. 

The  fact  that  a  circuit-breaker  may  be  designed  to  open  the  line  which 
it  connects,  whenever  the  direction  from  which  the  flow  of  energy  takes 
place  is  reversed,  is  taken  advantage  of  at  some  sub-stations  to  guard 
against  a  flow  of  energy  from  a  sub-station  back  toward  the  generating 
station.  By  this  means  a  flow  of  energy  from  a  sub-station  to  a  short 
circuit  in  one  of  the  lines  or  cables  connecting  it  with  the  generating  plant 
is  prevented. 


CHAPTER  XII. 

REGULATION  OF  TRANSMITTED  POWER. 

REGULATION  of  voltage  at  incandescent  lamps  is  a  serious  problem 
in  the  distribution  of  electrically  transmitted  energy.  Good  regulation 
should  not  allow  the  pressure  at  incandescent  lamps  rated  at  no  to 
1 20  volts  to  vary  more  than  one  volt  above  or  below  the  normal. 

Electric  motor  service  is  much  less  exacting  as  to  constancy  of  voltage, 
and  the  pressure  at  motor  terminals  may  sometimes  be  varied  as  much 
as  ten  per  cent  without  material  objection  on  the  part  of  users.  A  mixed 
service  to  these  three  classes  of  apparatus  must  often  be  provided 
where  transmitted  energy  is  used,  and  the  limitations  as  to  variations  at 
incandescent  lamps  are  thus  the  ones  that  must  control  the  regulation 
of  pressure. 

Transmission  systems  may  be  broadly  divided  into  those  that  have 
no  sub-stations  and  must  therefore  do  all  regulation  at  the  generating 
plant,  and  those  that  do  have  one  or  more  sub-stations  so  that  regulation 
of  voltage  may  be  carried  out  at  both  ends  of  the  transmission  line. 

As  a  rule,  a  sub-station  with  an  operator  in  attendance  is  highly 
desirable  between  transmission  and  distribution  lines,  and  this  is  the 
plan  generally  followed  at  important  centres  of  electrical  supply,  even 
though  the  transmission  is  a  short  one.  One  example  of  this  sort  may 
be  noted  at  Springfield,  Mass.,  where  energy  for  electrical  supply  is 
transmitted  from  two  water-power  plants  on  the  Chicopee  River  only 
about  four  and  a  half  and  six  miles,  respectively,  from  the  sub-station 
in  the  business  centre  of  the  city.  The  voltage  of  transmission  for  two- 
phase  current  in  this  case  is  6,000,  and  is  reduced  to  about  2,400  volts  at 
the  sub-station  for  the  general  distribution  of  light  and  power.  A  similar 
instance  may  be  seen  at  Concord,  N.  H.,  where  electrical  energy  at  both 
2,500  and  10,000  volts  is  delivered  to  a  sub-station  in  the  business  section 
from  a  water-power  plant  at  Sewall's  Falls,  on  the  Merrimac  River,  four 
and  one-half  miles  distant.  From  this  sub-station  the  current  is  dis- 
tributed at  about  2,500  volts  for  the  supply  of  lamps  and  motors.  A  sub- 


156    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


REGULATION  OF  TRANSMITTED  POWER. 


IS7 


station  was  found  desirable  at  Concord  for  purposes  of  regulation  before 
the  voltage  of  transmission  was  raised  above  that  of  distribution.  Sub- 
sequently, when  the  load  increased,  the  voltage  of  10,000  was  adopted  on 
a  part  of  the  transmission  circuit  in  order  to  avoid  an  increase  in  the  size 
of  their  conductors. 

In  some  instances,  however,  transmission  and  distribution  lines  are 


FIG.  65. -Area  of  Electrical  Distribution  at  Montreal. 

joined  without  the  intervention  of  a  sub-station,  where  regulation  of 
voltage  can  be  accomplished,  though  this  practice  has  little  to  recom- 
mend it  aside  from  the  savings  in  first  cost  of  installation  and  subsequent 
cost  of  operation.  These  savings  are  more  apparent  than  real  if  fairly 
constant  pressure  is  to  be  maintained  at  the  lamps,  because  what  is 
gained  by  the  omission  of  sub-stations  will  be  offset,  in  part  at  least,  by 
additional  outlays  on  the  lines  if  good  regulation  is  to  be  maintained. 
This  fact  may  be  illustrated  by  reference  to  Figs.  66,  67,  and  68,  in  each 


158     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

of  which  D  represents  a  generating  station  and  A,  B,  and  C  towns  or 
cities  where  energy  from  the  station  is  to  be  distributed.  In  the  case 
of  each  figure  it  is  assumed  that  the  distance  between  the  generating 
station  and  each  of  the  cities  or  towns  is  such  that  distributing  lines 
with  a  loss  of,  say,  not  more  than  two  per  cent  in  voltage  at  full  load 
cannot  be  provided  between  the  generating  station  and  each  city  or 
town  because  of  the  cost  of  conductors.  This  being  so,  one  or  more 


TRANSMITTED  Powi 
FIG.  66. 


TRAN8MITTED  POWER. 


FIG.  67. 


FIG.  68. 

centres  of  distribution  must  be  located  in  each  town,  and  the  trans- 
mission lines  must  join  the  distribution  lines  at  these  centres  either  on 
poles  or  in  sub-stations.  If  several  of  these  towns  are  in  the  same  gen- 
eral direction  from  the  generating  plant  so  as  to  be  reached  by  the  same 
transmission  line,  as  A ,  B,  and  C  in  Fig.  66,  this  one  line  will  be  all  that 
is  necessary  with  a  sub-station  in  each  town.  Where  sub-stations  are 
not  employed  a  separate  transmission  circuit  must  be  provided  between 
the  generating  plant  and  each  town  for  reasons  that  will  appear  presently. 
The  percentage  of  voltage  variation  in  a  transmission  line  under  changing 
loads  will  be  frequently  from  five  to  ten,  and  is  thus  far  beyond  the 
allowable  variations  at  incandescent  lamps.  To  give  good  lighting  ser- 


REGULATION  OF  TRANSMITTED  POWER.          159 

vice  the  centre  of  distribution,  where  the  transmission  line  joins  the  dis- 
tribution circuits,  must  be  maintained  at  very  nearly  constant  voltage  if 
no  sub-station  is  located  there.  Regulation  at  a  generating  station  will 
compensate  for  the  changing  loss  of  pressure  in  a  line  under  varying  loads 
so  as  to  maintain  a  nearly  constant  voltage  at  any  one  point  thereon.  No 
plan  of  station  regulation,  however,  can  maintain  constant  voltages  at 
several  points  on  the  same  transmission  line  when  there  is  a  varying  load 
at  each.  The  result  is  that  even  though  the  several  towns  served  are  in 
the  same  general  direction  from  the  generating  station,  as  in  Fig.  67,  yet 
each  town  should  have  its  separate  transmission  line  where  no  sub-sta- 
tions in  the  towns  are  provided.  In  the  case  illustrated  by  Fig.  68,  where 
the  towns  served  are  in  very  different  directions  from  the  generating 
station,  there  should  be  a  separate  transmission  line  to  each,  regard- 
less of  whether  there  is  a  sub-station  or  only  a  centre  of  distribution 
there. 

Even  in  the  case  illustrated  by  Fig.  68,  as  in  each  of  the  others,  there 
is  a  large  saving  effected  in  the  cost  of  distribution  lines  by  the  employ- 
ment of  a  sub-station  at  the  point  where  these  lines  join  the  trans- 
mission circuit,  provided  that  the  variation  of  pressure  at  lamp  terminals 
is  to  be  kept  within  one  volt  either  way  from  the  standard.  With  the 
variations  of  loads  the  loss  of  pressure  in  the  distribution  lines  will  range 
from  zero  to  its  maximum  amount  and  the  connected  lamps  will  be  sub- 
jected to  the  change  of  voltage  represented  by  this  total  loss,  unless  the 
distribution  start  from  a  sub-station  where  the  loss  in  distribution  lines 
can  be  compensated  for  by  regulation.  To  give  good  service  the  dis- 
tribution lines  should  be  limited  to  a  loss  of  one  per  cent  at  full  load  if 
there  is  no  sub-station  where  they  join  transmission  lines.  With  oppor- 
tunity for  regulation  at  a  sub-station  the  maximum  loss  in  distribution 
lines  may  easily  be  doubled,  thus  reducing  their  weight  by  one-half  in 
comparison  with  that  required  where  there  is  no  sub-station. 

Another  advantage  of  connecting  transmission  and  distribution  lines 
in  a  sub-station,  where  regulation  of  voltage  can  be  had,  lies  in  the  fact 
that  it  is  practically  impossible  to  maintain  an  absolutely  constant  press- 
ure miles  from  a  generating  plant  at  the  end  of  a  transmission  line  that 
is  carrying  a  mixed  and  varying  load.  A  result  is  that  without  the  in- 
tervention of  regulation  at  a  sub-station  it  is  almost  impossible  to  give 
good  lighting  service  over  a  long  transmission  line.  Furthermore,  the 
labor  of  regulation  at  a  generating  station  is  much  increased  where  there 
are  no  sub-stations,  because  it  must  be  much  more  frequent  and  accu- 
rate. The  absence  of  sub-stations  from  a  transmission  system  thus  im- 


160    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

plies  more  transmission  circuits,  heavier  distribution  circuits,  more  labor 
at  the  generating  plant,  and  a  poor  quality  of  lighting  service. 

Where  stationary  motors  form  the  great  bulk  of  the  load  on  a  trans- 
mission system,  and  good  lighting  service  is  of  small  importance,  it  may 
be  well  to  omit  sub-stations  at  some  centres  of  distribution.  This  is  a 
condition  that  sometimes  exists  in  the  Rocky  Mountain  region  where  the 
main  consumers  of  power  along  a  transmission  line  may  be  mines  or 
works  for  the  reduction  of  ores.  An  example  of  this  sort  exists  in  the 
system  of  the  Telluride  Power  Transmission  Company,  in  Utah,  which 
extends  from  Provo  Canon,  on  the  river  of  the  same  name,  entirely 
around  Utah  Lake  by  way  of  Mercur,  Eureka,  and  Provo,  and  back  to 
the  power-house  in  Provo  Canon,  a  continuous  circuit  of  105  miles. 

The  transmission  voltage  on  this  line  is  40,000,  and  at  intervals  where 
there  are  distributing  points  the  voltage  is  reduced  to  about  5,000  by 
transformers  on  poles,  and  without  the  aid  of  regulation  at  sub-stations 
in  some  cases.  The  power  thus  transmitted  is  largely  used  in  mines  and 
smelters  for  the  operation  of  motors,  but  also  for  some  commercial  light- 
ing. 

Regulation  at  generating  stations  of  the  voltage  on  transmission  lines 
may  be  accomplished  by  the  same  methods  whether  there  are  sub-sta- 
tions at  centres  of  distribution  or  not.  In  any  such  regulation  the  aim 
is  to  maintain  a  certain  voltage  at  some  particular  point  on  the  transmis- 
sion line,  usually  its  end,  where  the  distribution  circuits  are  connected. 
If  more  than  one  point  of  distribution  exists  on  the  same  transmission 
line,  the  regulation  at  the  generating  plant  must  be  designed  to  maintain 
the  desired  pressure  at  only  one  of  these  points,  leaving  regulation  at  the 
others  to  be  accomplished  by  local  means.  One  method  of  regulation 
consists  in  the  overcompounding  of  each  generator  so  that  the  voltage 
at  its  terminals  will  rise  at  a  certain  rate  as  its  load  increases.  If  a  gen- 
erator and  transmission  line  are  so  designed  that  the  rise  of  voltage  at 
the  generator  terminals  just  corresponds  with  the  loss  of  voltage  on  the 
line  when  the  output  of  that  generator  alone  passes  over  it  to  some  par- 
ticular point,  then  the  pressure  at  that  point  may  be  held  nearly  con- 
stant for  all  loads  if  no  energy  is  drawn  from  the  line  elsewhere.  These 
several  conditions  necessary  to  make  regulation  by  the  compounding  of 
generators  effective  can  seldom  be  met  in  practice.  If  a  varying  num- 
ber of  generators  must  work  on  the  same  transmission  line,  or  if  varying 
loads  must  be  supplied  at  different  points  along  the  line,  no  compound 
winding  of  generators  will  suffice  to  maintain  a  constant  voltage  at  any 
point  on  the  line  that  is  distant  from  the  power-station.  For  these  reasons 


REGULATION  OF  TRANSMITTED  POWER.          161 

the  compound  winding  of  generators  is  of  minor  importance  so  far  as  the 
regulation  of  voltage  on  transmission  lines  is  concerned,  and  on  large 
alternators  is  not  generally  attempted.  An  example  may  be  noted  on  the 
3,750-kilowatt  generators  at  Niagara  Falls,  where  the  single  magnet 
winding  receives  current  from  the  exciters  only. 

A  much  more  effective  and  generally  adopted  method  of  regulation 
of  voltage  at  the  generating  plants  of  transmission  systems  is  based  on 
the  action  of  an  attendant  who  varies  the  current  in  the  magnet  coils  of 
each  generator  so  as  to  raise  or  lower  its  voltage  as  desired.  The  regula- 
tion must  be  for  some  one  point  on  the  transmission  line,  and  the  attend- 
ant at  the  generating  plant  may  know  the  voltage  at  that  point  either  by 
means  of  a  pair  of  pressure  wires  run  back  from  that  point  to  a  voltmeter 
at  the  generating  plant,  by  a  meter  that  indicates  the  voltage  at  the  point 
in  question  according  to  the  current  on  the  line,  or  by  telephone  connec- 
tion with  a  sub-station  at  the  point  where  the  constant  voltage  is  to  be 
maintained.  Pressure  wires  are  a  reliable  means  of  indicating  in  the 
generating  station  the  voltage  at  a  point  of  distribution  on  the  line,  but 
the  erection  of  these  wires  is  quite  an  expense  in  a  long  transmission,  and 
in  such  cases  they  are  only  occasionally  used.  Owing  to  inductive  effects 
and  to  variable  power-factors  the  amperes  indicated  on  a  line  carrying 
alternating  current  are  far  from  a  certain  guide  as  to  the  drop  in  voltage 
between  the  generating  station  and  the  distant  point.  In  long  transmis- 
sions, telephone  communication  between  the  generating  plant  and  the 
sub-stations  is  the  most  general  way  in  which  necessary  changes  to 
maintain  constant  voltage  at  sub-stations  are  brought  to  the  attention 
of  the  attendant  in  the  generating  plant.  Few,  if  any,  extensive  trans- 
mission systems  now  operate  without  telephone  connection  between  a 
generating  plant  and  all  of  its  sub-stations,  or  between  a  single  sub-sta- 
tion and  the  several  generating  plants  that  may  feed  into  it.  Thus,  the 
generating  plant  at  Spier  Falls,  on  the  Hudson  River,  will  be  connected 
by  telephone  with  sub-stations  at  Schenectady,  Albany,  Troy,  and  some 
half-dozen  smaller  places.  On  the  other  hand,  the  single  sub-station  in 
Manchester,  N.  H.,  that  receives  the  energy  from  four  water-power  plants 
has  a  direct  telephone  line  to  each. 

Where  two  or  more  transmission  lines  from  the  same  power-station 
are  operated  from  the  same  set  of  bus-bars  the  voltage  at  a  distant  point 
on  each  line  cannot  be  held  constant  by  changes  of  pressure  on  these 
bus-bars.  One  generator  only  may  be  connected  to  each  transmission 
line  and  be  regulated  for  the  loss  on  that  line,  but  this  loses  the  ad- 
vantages of  multiple  operation.  Another  plan  is  to  connect  a  regula- 
1 1 


162     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

tor  in  each  transmission  line  before  it  goes  from  the  generating  plant, 
One  type  of  regulator  for  this  purpose  consists  of  a  transformer  with 
its  secondary  coil  divided  into  a  number  of  sections  and  the  ends  of 
these  sections  brought  out  to  a  series  of  contact  segments.  The  pri- 
mary coil  of  this  transformer  may  be  supplied  with  current  from  the 
bus-bars  and  the  secondary  coil  is  then  connected  in  series  with  the 
line  to  be  regulated,  so  that  the  secondary  voltage  is  added  to  or  sub- 
tracted from  that  of  the  main  circuit.  A  movable  contact  arm  on  the 
segments  to  which  the  sections  of  the  secondary  coil  are  connected  makes 
it  possible  to  vary  the  secondary  voltage  by  changing  the  number  of  these 
sections  in  circuit.  In  another  transformer  used  for  regulating  purposes 
the  primary  coil  is  connected  to  the  bus-bars  as  before  and  the  movable 
secondary  coil  is  put  in  series  with  the  line  to  be  regulated.  The  regula- 
tion is  accomplished  in  this  case  by  changing  the  position  of  the  secondary 
relative  to  that  of  the  primary  coil  and  thus  raising  or  lowering  the  sec- 
ondary voltage.  Both  of  these  regulators  require  hand  adjustment,  and 
the  attendant  may  employ  the  telephone,  pressure  wires,  or  the  compen- 
sating voltmeter  above  mentioned,  to  determine  the  voltage  at  the  centre 
of  distribution.  The  voltage  indicated  by  this  so-called  "compensator" 
is  that  at  the  generating  station  minus  a  certain  amount  which  varies  with 
the  current  flowing  in  the  line  to  be  regulated.  The  voltmeter  coil  of 
the  compensator  is  connected  in  series  with  the  secondary  coils  of  two 
transformers,  which  coils  work  against  each  other.  One  transformer  has 
its  secondary  coil  arranged  to  indicate  the  full  station  voltage,  and  the 
other  secondary  coil  is  actuated  by  a  primary  coil  that  carries  the  full 
current  of  the  regulated  line.  By  a  series  of  contacts  the  effect  of  this 
last-named  coil  can  be  varied  to  correspond  with  the  number  of  volts  that 
are  to  be  lost  at  full  load  between  the  generating  station  and  the  point 
on  the  transmission  line  at  which  the  voltage  is  to  be  held  constant.  If 
there  is  no  inductive  drop  on  the  transmission  line,  or  if  this  drop  is  of 
known  and  constant  amount,  the  compensator  may  give  the  actual  volt- 
age at  the  point  for  which  the  regulation  is  designed. 

Automatic  regulators  are  used  in  some  generating  stations  to  maintain 
a  constant  voltage  either  at  the  generating  terminals  or  at  some  distant 
distributing  point  on  a  line  operated  by  a  single  generator.  These  regu- 
lators may  operate  rheostats  that  are  in  series  with  the  magnet  windings 
of  the  generators  to  be  regulated,  and  raise  or  lower  the  generator  voltage 
by  varying  the  exciting  current  in  these  windings.  These  regulators  are 
much  more  effective  to  maintain  constant  voltage  at  generating  stations 
than  at  the  distributing  end  of  long  transmission  lines  with  variable, 


REGULATION  OF  TRANSMITTED  POWER. 


163 


power-factors.  In  spite  of  the  compound  winding  of  generators,  of  auto- 
matic regulators  for  the  exciting  currents  in  their  magnet  coils,  and  of 
regulating  transformers  in  the  transmission  circuits,  hand-adjustment  of 
rheostats  in  series  with  the  magnet  coils  of  generators  remains  the  most 
generally  used  at  the  generating  stations  of  long  transmission  systems. 
Automatic  regulators  at  the  ends  of  transmission  lines  in  sub-stations  are 
now  being  introduced,  and  may  prove  very  desirable. 

The  more  exacting  and  final  work  of  regulation  in  transmission  sys- 
tems is  usually  done  at  the  sub-stations.     After  a  nearly  constant  voltage 


FIG.  69.— Motor-generators  in  Shawinigan  Sub-station  at  Montreal. 

is  delivered  at  the  high-pressure  coils  of  step-down  transformers  in  a 
sub-station,  there  remains  the  varying  losses  in  these  transformers,  in 
motor-generators  or  converters,  in  distribution  lines  and  in  service  trans- 
formers, to  be  compensated  for.  In  general,  three  or  four  sorts  of  loads 
must  be  provided  for,  namely,  arc  or  incandescent  lamps  for  street  light- 
ing on  series  circuits,  usually  of  4,000  to  10,000  volts.  Arc  and  incandes- 
cent lamps  on  constant-pressure  circuits  of  2,000  to  2,500  volts  for  com- 
mercial lighting,  direct-current  stationary  motors  on  constant-pressure 
circuits  of  about  500  volts,  and  alternating  motors  which  may  be  served 
at  either  2,500  or  500  volts  according  to  their  sizes  and  locations.  To 
these  loads  may  be  added  that  of  street-car  motors  of  500  volts,  direct 
current.  Both  the  stationary  and  the  street-car  motors,  but  more  es- 


164    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


pecially  the  latter,  by  their  changes 
of  load  give  rise  to  large  and  rapid 
fluctuations  of  voltage  on  the  distri- 
bution lines  to  which  they  are  con- 
nected. The  problem  of  regulation 
with  combined  lamp  and  motor  loads 
is  not,  therefore,  so  much  to  maintain  a 
nearly  constant  voltage  at  the  motors 
as  to  protect  the  lamps  from  the  fluctua- 
tions of  vol  tage  which  th  e  moto  rs  set  up . 
For  street-car  motors  using  direct 
current  at  about  500  volts,  the  sub- 
station equipment  includes  either  step- 
down  transformers  and  converters 
or  motor-generators  with  or  without 
transformers.  It  is  the  practice  in 
some  cases  where  both  lighting  and 
street-railway  service  are  drawn  from 
the  same  transmission  system  to  keep 
these  two  kinds  of  service  entirely 
separate,  devoting  independent  gen- 
erators and  transmission  lines,  as  well 
as  independent  transformers  and  con- 
verters or  motor-generators,  to  the 
street-car  work.  'This  is  done  in 
the  transmission  system  centring  at 
Manchester,  N.  H.,  in  which  each 
one  of  the  four  water-power  plants, 
as  well  as  the  sub-station,  has  a 
double  set  of  bus-bars  on  the  switch- 
board; and  from  each  water-power 
plant  to  the  sub-station  there  are  two 
transmission  circuits.  In  operation, 
.one  set  of  generators,  bus-bars,  trans- 
mission circuits,  and  transformers 
supply  converters  or  motor-generators 
for  the  street-car  motors;  and  another 
set  of  generators,  bus-bars,  trans- 
mission circuits,  and  transformers  are 
devoted  to  lighting  and  stationary 


REGULATION  OF  TRANSMITTED  POWER.  165 

motors  in  this  system.  Where  street-car  motors  draw  their  energy  from 
the  same  generators  and  transmission  lines  that  supply  commercial  in- 
candescent lamps,  some  means  must  be  adopted  to  protect  the  lighting 
circuits  from  the  fluctuations  of  voltage  set  up  by  the  varying  street-car 
loads.  One  way  to  accomplish  this  purpose  is  to  operate  the  lighting 
circuits  with  generators  driven  by  synchronous  motors  in  the  sub-stations. 
These  generators  may,<cf  course,  be  of  either  direct  or  alternating  type 
and  of  any  desired  voltage.  The  synchronous  motors  driving  these 
generators  take  their  current  from  the  transmission  line  either  with  or 
without  the  intervention  of  step-down  transformers.  By  this  use  of  syn- 
chronous motors  the  lighting  circuits  escape  fluctuations  of  voltage  cor- 
responding to  those  on  the  transmission  line,  because  synchronous  motors 
maintain  constant  speeds  independently  of  the  voltage  of  the  circuits  to 
which  thev  are  connected.  This  plan  was  followed  at  Buffalo,  where  the 
street-car  system  and  the  lighting  service  are  operated  with  energy  from 
the  Niagara  Falls  stations  over  the  same  transmission  line.  In  one  of 
the  sub-stations  at  Buffalo,  both  2, 200- volt,  two-phase  alternators,  and 
1 50- volt  continuous-current  generators  for  lighting  service,  are  driven  by 
synchronous  motors  connected  to  the  Niagara  transmission  line  through 
transformers.  At  other  sub-stations  in  Buffalo,  the  5QO-volt  continuous 
current  for  street-car  motors  is  obtained  from  the  same  transmission  sys- 
tem through  transformers  and  converters.  Another  solution  of  the  prob- 
lem of  voltage  regulation  where,  street-railway  and  commercial  lighting 
service  are  to  be  drawn  from  the  same  transmission  line  is  found  in  the 
operation  of  5oo-volt  continuous-current  generators  in  the  sub-stations 
by  synchronous  motors  fed  from  the  line  either  directly  or  through  trans* 
formers.  This  plan  has  been  adopted  in  the  transmission  system  of  the 
Boston  Edison  Company,  which  extends  to  a  number  of  cities  and  towns 
within  a  radius  of  twenty-five  miles.  The  sub-stations  at  Natick  and 
Woburn  in  this  system,  where  there  are  street-railway  as  well  as  light- 
ing loads,  contain  5oo-volt  continuous-current  generators  driven  by  syn- 
chronous motors  connected  directly  to  the  three-phase  transmission  lines. 
In  a  case  like  this  the  synchronous  motors  maintain  their  speed  irrespec- 
tive of  the  voltage  on  the  line  and  thus  tend  to  hold  that  voltage  steady 
in  spite  of  the  variable  losses  due  to  fluctuating  loads. 

Stationary  motors  should  not  as  a  rule  be  operated  from  the  same 
distribution  lines  that  supply  incandescent  lamps,  especially  in  sizes 
above  one  horse-power,  and  this  is  the  better  practice.  Motor  circuits 
of  about  2,400  volts  and  two-  or  three-phase,  alternating,  or  500  volts, 
alternating  or  direct  current,  may  be  supplied  at  a  sub-station  either 


i66     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

by  transformers  alone  in  the  first  case  or  by  transformers  and  converters 
in  the  second.  In  either  case  no  especial  provision  is  usually  neces- 
sary for  the  regulation  of  constant  pressure  on  the  motor  circuits. 

In  some  transmission  systems  the  distribution  circuits  for  stationary 


motors  are  not  fed  by  the  same  transmission  lines  that  carry  the  light- 
ing load,  but  draw  their  energy  from  lines  that  do  no  other  work.  This 
practice  is  certainly  desirable,  as  it  frees  the  lighting  circuits  from  all 
fluctuations  of  voltage  due  to  line  losses  with  changing  motor  loads. 
Examples  of  this  sort  may  be  seen  at  Springfield,  Mass.,  and  Portland 


REGULATION  OF  TRANSMITTED  POWER.          167 

and  Lewiston,  Me.,  in  each  of  which  the  load  of  stationary  motors  is 
operated  over  independent  transmission  as  well  as  distribution  lines. 

In  transmission  systems  series  arc  and  incandescent  lamps  for  street 
lighting  are  commonly  operated  either  by  direct-current  arc  dynamos  or 
by  constant-current  transformers  or  constant-pressure  transformers  with 
automatic  regulators  at  the  sub-stations.  The  arc  dynamos  are  driven 
by  either  induction  or  synchronous  motors  supplied  directly  from  the 
transmission  line  or  through  transformers.  As  the  arc  dynamos  regulate 
automatically  for  constant  current  no  further  regulation  is  required.  If 
the  series  arc  and  incandescent  lamps  are  to  be  supplied  with  alternating 
current,  the  constant-current  transformer  or  the  constant-current  regu- 
lator come  into  use.  This  type  of  transformer  and  regulator  alike  de- 
pend for  their  regulating  effect  on  the  movement  of  a  secondary  coil  on 
a  transformer  core  in  such  a  way  that  the  current  in  this  coil,  which  is  in 
series  with  the  lamps,  is  held  nearly  constant.  Such  constant-current 
transformers  and  regulators  are  usually  supplied  from  the  transmission 
line  through  regular  constant-pressure  transformers,  and  they  hold  their 
currents  sufficiently  constant  for  the  purposes  of  their  use. 

The  main  problem  of  regulating  thus  comes  back  to  the  250-  or 
2,2oo-volt,  constant-pressure  circuits  for  incandescent  lighting,  supplied 
from  transmission  lines  through  transformers  or  motor  generators  or  both 
at  the  sub-station.  For  this  regulation  one  of  the  most  reliable  instru- 
ments is  the  hand  of  a  skilful  attendant,  guided  by  voltmeters  connected 
with  pressure  wires  from  minor  centres  of  distribution,  and  adjusting  the 
regulating  transformers  above  mentioned,  or  other  regulating  devices. 


CHAPTER  XIII. 

GUARD  WIRES  AND  LIGHTNING  ARRESTERS. 

LIGHTNING  in  its  various  forms  is  the  greatest  danger  to  which  trans- 
mission systems  are  exposed,  and  it  attacks  their  most  vulnerable  point, 
that  is,  insulation.  The  lesser  danger  as  to  lightning  is  that  it  will  punc- 
ture the  line  insulators  and  shatter  or  set  fire  to  the  poles.  The  greater 
danger  is  that  the  lightning  discharge  will  pass  along  the  transmission 
wires  to  stations  and  sub-stations  and  will  there  break  down  the  insula- 
tion of  generators,  motors,  or  transformers.  Damage  by  lightning  may 
be  prevented  in  either  of  two  ways,  that  is,  by  shielding  the  transmission 
line  so  completely  that  no  form  of  lightning  charge  or  discharge  can  reach 
it,  or  by  providing  so  easy  a  path  from  line  conductors  to  earth  that 
lightning  reaching  these  conductors  will  follow  the  intended  path  instead 
of  any  other.  In  practice  the  shielding  effect  is  sought  by  grounded 
guard  wires,  and  the  easy  path  for  discharge  takes  the  form  of  lightning 
arresters,  but  neither  of  these  devices  is  entirely  effective. 

Aerial  transmission  lines  are  exposed  to  direct  discharges  of  lightning, 
to  electromagnetic  charges  due  to  lightning  discharges  near  by,  and  to 
electrostatic  charges  that  are  brought  about  by  contact  with  or  induction 
from  electrically  charged  bodies  of  air.  It  is  evidently  impracticable  to 
provide  a  shield  that  will  free  overhead  lines  from  all  these  influences. 
To  cut  off  both  electrostatic  and  electromagnetic  induction  from  a  wire 
and  also  to  free  it  from  a  possible  direct  discharge  of  lightning,  it  seems 
that  it  would  at  least  be  necessary  completely  to  incase  the  wire  with  a 
thick  body  of  conducting  material.  This  condition  is  approximated  when 
an  electric  circuit  is  entirely  beneath  the  surface  of  the  ground,  but  would 
be  hard  to  maintain  with  bare  overhead  wires.  It  seems,  however,  that 
grounded  guard  wires  near  to  and  parallel  with  long  aerial  circuits  should 
tend  to  discharge  any  high  electrostatic  pressures  existing  in  the  surround- 
ing air,  and  materially  to  reduce  the  probability  that  a  direct  discharge 
of  lightning  will  choose  the  highly  insulated  circuits  for  its  path  to 
earth.  Lightning  arresters  may  conduct  induced  and  direct  lightning 
discharges  to  earth,  without  damage  to  transmission  lines,  so  that  both 
arresters  and  guard  wires  may  logically  be  used  in  the  same  system. 

1 68 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      169 

Wide  differences  of  opinion  exist  as  to  the  general  desirability  of 
grounded  guard  wires  on  transmission  lines,  both  because  of  their  un- 
doubted disadvantages  and  because  the  degree  of  protection  that  they 
afford  is  uncertain.  It  seems,  however,  that  the  defects  of  guard  wires 
depend  in  large  degree  on  the  kind  of  wire  used  for  the  purpose,  and 
the  method  of  its  erection.  Galvanized  iron  wire  with  barbs  every 
few  inches  has  been  more  generally  used  for  guard  wires  along  trans- 
mission lines  than  any  other  sort.  Sometimes  a  single  guard  wire  of 
this  sort  has  been  run  on  a  pole  line  carrying  transmission  circuits, 
and  the  more  common  location  of  this  single  wire  is  on  the  tops  of  the 
poles.  In  other  cases  two  guard  wires  have  been  used  on  the  same  pole 
line,  one  of  these  wires  being  located  at  each  end  of  the  highest  cross- 
arm  and  outside  of  the  power  wires.  Besides  these  guard  wires  at  the 
ends  pf  the  top  cross-arms  of  a  pole  line,  a  third  wire  has  in  some  systems 
been  added  to  the  tops  of  the  poles.  These  guard  wires  have  sometimes 
been  secured  to  the  poles  and  cross-arms  by  iron  staples  driven  over  the 
wire  and  into  the  wood,  and  in  other  cases  the  guard  wires  are  mounted 
on  small  glass  insulators.  Much  variation  in  practice  also  exists  as  to 
the  ground  connections  of  guard  wires,  !?uch  connections  being  made  at 
every  pole  in  some  systems,  and  much  less  frequently  in  some  others. 

With  all  these  differences  in  the  practical  application  of  guard  wires 
it  is  not  strange  that  opinions  as  to  their  utility  do  not  agree.  Further 
reason  for  differences  of  opinion  as  to  the  practical  value  of  guard  wires 
exists  in  the  fact  that  in  some  parts  of  the  country  the  dangers  from  light- 
ning are  largely  those  of  the  static  and  inductive  sort,  that  are  most  effec- 
tively provided  for  by  lightning  arresters,  while  in  other  parts  of  the 
country  direct  lightning  strokes  are  the  greatest  menace  to  transmis- 
sion systems.  At  the  present  time,  knowledge  of  the  laws  governing 
the  various  manifestations  of  energy  that  are  known  under  the  general 
head  of  lightning  is  imperfect,  and  the  most  reliable  rules  for  the  use 
of  guard  wires  along  transmission  lines  aTe  those  derived  from  practical 
experience. 

A  case  where  a  guard  wire  did  not  prove  effective  as  a  protection 
against  lightning  is  that  of  the  San  Miguel  Consolidated  Gold  Mining 
Company,  of  Telluride,  Col,  whose  three  transmission  lines  ran  from  the 
water-power  plant  to  points  from  three  to  ten  miles  distant,  as  described 
in  A.  I.  E.  E.,  vol.  xi.,  p.  337,  and  following  pages.  This  transmission 
operated  at  3,000  volts,  single-phase,  alternating,  and  the  pole  lines  ran 
over  the  mountains  at  elevations  of  8,800  to  12,000  feet  above  sea-level, 
passing  across  bare  ridges  and  tracts  of  magnetic  material.  It  was  stated 


i yo    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

that  the  country  over  which  the  circuits  ran  is  so  dry  and  rocky  that  it 
was  practically  impossible  to  secure  good  ground  connections  along  the 
line,  and  no  mention  was  made  of  the  way  in  which  the  ground  wire  was 
grounded,  or  of  the  number  of  its  ground  connections.  Furthermore,  it 
does  not  appear  that  there  was  more  than  one  guard  wire  on  each  pole 
line.  Under  these  circumstances,  and  with  a  certain  make  of  lightning 
arresters  in  use  at  the  station,  lightning  was  a  frequent  cause  of  damage 
to  the  connected  apparatus.  The  insulation  of  some  of  the  machinery 
is  described  as  honeycombed  with  perforations  which  led  to  continual 
leakage,  grounds,  and  short-circuits,  which  seems  to  indicate  that  the 
damage  was  being  done  by  static  and  inductive  discharges  rather  than 
by  direct  lightning  strokes,  one  of  which  would  have  disabled  a  ma- 
chine at  once.  The  .type  of  lightning  arrester  in  use  on  this  system  was 
changed,  and  thorough  ground  connections  were  provided  for  the  new 
arresters,  after  which  the  damage  by  lightning  came  to  an  end.  It  is  not 
stated,  however,  that  the  guard  wires  were  removed.  This  case  has  been 
referred  to  as  one  in  which  guard  wires  failed  to  give  protection,  but,  as 
may  be  seen  from  the  above  facts,  such  a  statement  is  hardly  fair.  In 
the  first  place,  it  does  not  appear  that  the  single  guard  wire  on  each  pole 
line  was  effectively  grounded  anywhere.  Again,  a  large  part  of  the 
damage  to  apparatus  appears  to  have  been  the  result  of  static  or  induc- 
tive discharges  that  could  not  in  the  nature  of  things  have  been  pre- 
vented by  a  guard  wire.  Finally,  as  the  guard  wire  was  not  removed 
after  the  new  lightning  arresters  were  erected,  it  is  possible  that  this  wire 
prevented  some  direct  discharges  over  the  transmission  wires  that  would 
have  been  destructive. 

On  page  381  of  the  volume  of  A.  I.  E.  E.  above  cited,  it  is  stated  that 
the  frequency  and  violence  of  lightning  discharges  that  entered  a  certain 
electric  station  on  Staten  Island  were  much  less  after  guard  wires  had 
been  erected  along  the  connected  circuits  than  they  were  before  the  guard 
wires  were  put  up. 

It  is  also  stated  on  page  385  of  the  same  volume  that  examination  of 
statistics  of  a  number  of  stations  in  this  country  and  Europe  had  shown 
that  in  every  case  where  an  overhead  guard  wire  had  been  erected  over 
power  circuits,  or  where  these  circuits  ran  for  their  entire  distance  beneath 
telegraph  wires,  lightning  had  given  no  trouble  on  the  circuits  so  pro- 
tected. Unfortunately,  the  speaker  who  made  this  statement  did  not  tell 
us  where  the  interesting  statistics  mentioned  could  be  consulted. 

On  the  first  pole  line  erected  for  power  transmission  from  Niagara 
Falls  to  Buffalo,  two  guard  wires  were  strung  at  opposite  ends  of  the  top 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      171 

cross-arm  on  guard  irons  there  located.  This  cross-arm  also  carried  parts 
of  two  power  circuits,  and  the  nearest  wires  of  these  circuits  were  distant 
about  thirteen  inches  from  the  guard  irons.  These  guard  wires  were 
barbed,  and  grounded  at  every  fifth  pole,  according  to  an  account  given  in 
A.  I.  E.  E.,  vol.  xviii.,  at  514  and  following  pages.  The  character  of  the 
ground  connections  is  not  stated.  Much  trouble  in  the  way  of  grounds 
and  short  circuits  on  the  transmission  lines  was  caused  by  these  guard 
wires  at  times  when  they  were  broken  by  the  weight  of  ice  coatings  and 
wind  pressure.  As  a  result  of  these  troubles  the  guard  wires  were  re- 
moved in  1898.  Since  that  date  it  appears  that  the  transmission  lines 
between  Niagara  Falls  and  Buffalo  have  been  without  guard  wires.  Up 
to  1901,  according  to  page  537  in  the  volume  just  cited,  twenty  per  cent 
of  the  interruptions  in  operation  at  the  Niagara  plant  were  caused  by 
lightning,  and  it  seems  probable  that  this  record  applies  to  the  period 
after  1898,  when  the  guard  wires  were  removed.  It  is  also  stated  that 
during  a  single  storm  the  line  was  struck  five  times,  and  that  five  poles 
with  their  cross-arms  were  destroyed.  If  these  direct  lightning  strokes 
occurred  while  there  were  no  guard  wires  along  the  line,  as  seems  to 
have  been  the  fact,  it  is  a  fair  question  whether  such  wires  well 
grounded  would  not  have  carried  off  the  discharges  without  damage. 
In  California,  the  country  of  long  transmissions,  the  use  of  guard 
wires  along  the  pole  lines  is  quite  general.  Many  of  these  lines  run 
east  and  west  across  the  State,  and  a  single  line  may  thus  have  eleva- 
tions in  its  different  parts  all  the  way  from  that  of  tide-water  up  to 
several  thousand  feet  above  sea-level.  Unless  guard  wires  are  strung 
with  these  lines  there  is  much  manifestation  of  induced  or  static  elec- 
tricity, according  to  an  account  at  page  538,  in  vol.  xviii.,  A.  I.  E.  E., 
where  it  is  said  that  in  the  absence  of  guard  wires  a  person  will  be 
knocked  off  his  feet  every  time  he  touches  a  transmission  wire  that  is 
entirely  disconnected  from  the  source  of  power.  It  is  also  said  that  this 
static  charge  on  idle  power  lines  is  sufficient,  in  time,  to  puncture  the 
insulation  of  the  connected  apparatus.  On  the  other  hand,  where  the 
grounded  and  barbed  guard  wires  are  strung  over  the  entire  lengths  of 
these  long  power  lines,  these  lines  may  be  handled  with  impunity  when 
they  are  idle.  Ground  connections  to  the  guard  wire  are  said  to  be 
made  at  about  every  fourth  pole,  and  to  consist  of  a  wire  stapled  down 
the  face  of  the  pole  and  joined  to  an  iron  plate  beneath  its  butt.  The 
barbed  guard  wire  itself,  of  which  each  pole  line  appears  to  have  but 
one,  is  regularly  stapled  to  the  tops  of  the  poles. 

At  the  reference  just  named  it  is  related  that  on  a  certain  transmission 


172     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

line  running  east  and  west  across  the  State  for  a  distance  of  forty-six 
miles,  and  protected  by  a  guard  wire,  no  trouble  was  experienced  during 
a  severe  storm  that  swept  north  and  south  over  the  line.  Meantime  the 
damage  on  other  lines  in  the  same  neighborhood,  and  presumably  not 
protected  by  guard  wires,  was  large. 

Between  the  electric  plant  at  Chambly,  on  the  Richelieu  River,  and 
Montreal,  Quebec,  a  distance  of  16.6  miles,  a  transmission  line  of  three 
circuits  on  two  pole  lines,  with  guard  wires,  was  operated  from  some  time 
in  1898  to  December  ist,  1902,  or  somewhat  more  than  four  years.  On 
the  date  last  named  the  dam  that  maintained  the  head  of  water  at  the 
Chambly  station  gave  way,  and  the  plant  was  shut  down  during  nearly 

Guard  wires. 


FIG.  72.— Transposition  of  Wires  on  Chambly  Montreal  Line. 

a  year  for  repairs.  For  as  much  as  three  years  this  line  was  operated  at 
12,000  volts,  sixty-six  cycles  per  second,  two-phase.  During  the  re- 
mainder of  the  period  up  to  the  failure  of  the  dam  the  line  was  operated 
at  25,000  volts,  sixty-three  cycles,  three-phase.  In  each  transmission 
two  pole  lines  were  employed  with  two  cross-arms  per  pole.  One  two- 
phase,  four- wire  circuit  was  carried  on  each  of  three  of  these  cross-arms. 
At  each  end  of  the  upper  cross-arm  on  each  pole,  and  at  a  distance  of 
fifteen  inches  from  the  nearest  power  wire,  a  guard  wire  was  mounted 
on  a  glass  insulator.  A  third  guard  wire  was  mounted  on  a  glass  insula- 
tor at  the  top  of  each  pole,  and  this  third  guard  wire  was  about  twenty 
inches  from  the  nearest  power  wire.  Each  of  these  guard  wires  was  made 
up  of  two  No.  12  B.  W.  G.  galvanized  iron  wires  twisted  together,  with 
a  four-point  barb  every  five  inches  of  length.  Poles  carrying  these  lines 
were  ninety  feet  apart,  and  at  each  pole  all  three  of  the  guard  wires  were 
connected  by  soldered  joints  to  a  ground  wire  that  was  stapled  down  the 
side  of  the  pole,  passed  through  an  iron  pipe  eight  feet  long,  and  was  then 
twisted  several  times  about  the  butt  of  the  pole  before  it  was  set  in  the 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      173 

ground.  At  three  points  along  the  line  the  conductors  consisted  of  sin- 
gle-conductor underground  or  submarine  cables  that  had  an  aggregate 
length  of  about  twenty-five  miles.  No  lightning  arresters  were  employed 
at  the  points  where  the  overhead  transmission  wires  joined  the  under- 
ground cables. 

These  two-phase,  12,000- volt  circuits  were  operated  from  some  time 
in  1898  to  some  time  in  1902,  and  during  that  time  there  was  no  damage 
done  by  lightning  either  at  the  Chambly  plant,  on  the  overhead  line  or 
the  underground  cable,  or  at  the  Montreal  sub-station.  This  record  is 
not  due  to  lack  of  thunder-storms,  for  in  the  territory  where  the  line 
is  located  these  storms  are  frequent  and  severe.  One  very  severe  storm 
during  the  period  in  question  resulted  in  serious  damage  on  distribution 
lines  at  Chambly  and  Montreal,  where  the  guard  wires  were  not  in  use, 
but  the  transmission  line  and  its  connected  apparatus  escaped  unharmed. 
The  path  of  this  storm  was  in  the  direction  of  the  transmission  line  from 
Montreal  to  Chambly,  and  several  trees  were  struck  on  the  way.  At 
the  time  of  this  storm  and  during  an  entire  summer  there  were  no  light- 
ning arresters  in  the  power-house  at  Chambly. 

In  1902,  when  the  transmission  line  just  considered  was  changed  from 
two-phase  to  three-phase,  and  its  voltage  raised  from  12,000  to  25,000, 
the  method  of  protection  by  grounded,  barbed  guard  wires,  as  above 
described,  was  retained.  Two  three-phase  circuits  were  arranged  on 
each  of  the  two  pple  lines,  with  one  wire  of  each  circuit  on  an  upper 
cross-arm  and  two  wires  of  each  circuit  on  a  lower  cross-arm,  so  that  the 
nearest  power  wire  on  the  upper  cross-arm  is  thirty-two  inches  from  the 
guard  wire,  and  the  nearest  power  wire  on  the  lower  cross-arm  is  about 
thirty  inches  from  the  guard  wire  at  each  end  of  the  upper  cross-arm. 
The  guard  wire  at  the  tops  of  the  poles  is  about  thirty-three  inches  from 
each  of  the  power  wires  on  the  upper  cross-arm.  In  this  three-phase  line 
there  is  about  1,440  feet  of  three-conductor  underground  cable,  and  this 
cable  lies  between  the  end  of  the  overhead  line  and  the  sub-station  in 
Montreal.  At  the  juncture  of  the  overhead  line  and  the  cables  there  is 
a  terminal  house  containing  lightning  arresters,  and  there  are  also  arrest- 
ers at  the  Chambly  plant  and  the  Montreal  sub-station.  No  lightning 
arresters  are  connected  to  this  line  save  those  at  the  generating  plant,  the 
terminal  house  and  the  sub-station. 

During  that  part  of  the  year  1902  in  which  the  new  25,ooo-volt  line 
was  in  operation — that  is,  after  the  change  and  up  to  the  time  of  the  failure 
of  the  dam — this  line  and  its  connected  apparatus  were  not  damaged 
in  any  way  by  lightning,  and  the  same  is  true  for  the  period  in  which  the 


174     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

line  was  idle  pending  repairs  on  the  dam.  The  experience  on  this  Mon- 
treal and  Chambly  transmission  is  probably  among  the  best  evidence  to 
be  found  anywhere  as  to  the  degree  of  protection  from  lightning  that 
may  be  had  by  the  use  of  guard  wires.  In  spite  of  cases  like  that  just 
considered,  where  guard  wires  appear  to  have  given  a  large  degree  of 
protection  to  transmission  systems,  many  important  transmissions  are 
operated  without  them. 

An  example  of  this  sort  may  be  seen  in  the  transmission  line  between 
the  io,ooo-horse-power  plant  at  Electra,  in  the  Sierra  Nevada  Mountains 
of  California,  and  San  Francisco,  a  distance  of  1 54  miles,  where  it  seems 
that  no  guard  wires  are  in  use.  Another  important  transmission  line 
that  appears  to  get  along  without  guard  wires  is  that  between  the  10,000- 
horse-power  plant  at  Canon  Ferry,  on  the  Missouri  River,  and  Butte, 
Mont.,  sixty-five  miles  away.  On  the  transmission  line  between  the 
power-station  on  Apple  River,  in  Wisconsin,  and  the  sub-station  at  St. 
Paul,  Minn.,  about  twenty-seven  miles  long,  there  are  no  guard  wires 
for  lightning  protection.  Further  east,  on  the  large,  new  transmission 
system  that  stretches  from  Spier  Falls  and  Glens  Falls  on  the  north  to 
Albany  on  the  south,  a  distance  in  a  direct  line  of  forty  miles,  no  guard 
wires  are  employed.  On  its  way  the  transmission  system  just  named 
touches  Saratoga,  Schenectady,  Mechanicsville,  Troy,  and  a  number  of 
smaller  places,  thus  forming  a  network  with  several  hundred  miles  of 
overhead  wire.  Examples  of  this  sort  might  be  multiplied,  but  those 
already  named  are  sufficient  to  show  that  it  is  entirely  practicable  to 
operate  long  transmission  systems  without  guard  wires  as  a  protection 
against  lightning. 

With  these  examples  of  transmission  systems  both  with  and  without 
guard  wires,  the  expediency  of  their  use  on  any  particular  line  should  be 
determined  by  weighing  their  supposed  advantages  against  their  known 
disadvantages,  under  the  existing  conditions.  It  seems  fairly  certain 
from  all  the  evidence  at  hand  that  if  guard  wires  are  to  offer  any  large 
degree  of  protection  to  transmission  systems  such  wires  must  be  fre- 
quently and  effectively  grounded.  There  is  certainly  some  reason  to 
think  that  the  failures  of  guard  wires  to  protect  transmission  systems  in 
some  instances  may  have  been  due  to  the  lack  of  numerous  and  effective 
ground  connections.  Such,  for  example,  may  have  been  the  case  above 
mentioned,  at  Telluride,  Col.  On  the  other  hand,  it  seems  reasonable 
to  believe  that  the  apparently  high  degree  of  protection  afforded  by  the 
guard  wires  on  the  Chambly  and  Montreal  line  is  due  to  the  fact  that 
these  wires  are  connected  through  soldered  joints  at  every  pole  with  a 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      175 

ground  wire  that  is  wound  about  its  base.  The  nearer  the  guard  wires 
are  located  to  the  power  wires  on  a  line  the  greater  is  the  danger  that 
a  guard  wire  will  come  into  contact  with  a  power  wire  by  breaking  or 
otherwise.  It  is  probable  that  the  protection  given  by  a  guard  wire 
does  not  increase  nearly  as  fast  as  the  distance  between  it  and  a  power 
wire  is  diminished.  Even  if  one  guard  wire  on  a  line  is  thought  to  be 
desirable,  it  does  not  follow  that  two  or  more  such  wires  should  be  used, 
for  the  additional  protection  given  by  two  or  three  guard  wires  beyond 
that  given  by  one  wire  may  be  trifling,  while  the  cost  of  erection  and  the 
danger  of  crosses  with  the  power  circuits  increase  directly  with  the  num- 
ber of  guard  wires.  At  one  time  it  was  thought  very  desirable  to  have 
barbs  on  guard  wires,  but  now  the  better  opinion  seems  to  be  that,  as 
barbs  tend  to  weaken  the  wire,  they  lead  to  breaks  and  cause  more 
trouble  than  they  are  worth.  The  point  where  the  barbs  are  located 
seems  to  rust  more  quickly  than  do  other  parts  of  the  wire.  In  some 
cases  barbed  guard  wires  that  have  given  trouble  by  breaking  have  been 
taken  down  and  smooth  wires  put  up  instead.  If  a  guard  wire  is  well 
grounded  at  least  as  often  as  every  other  pole,  its  size  may  be  determined 
largely  on  considerations  of  mechanical  strength  and  lasting  qualities. 
For  ordinary  spans  a  No.  4  B.  &  S.  G.  galvanized  soft  iron  wire  seems 
to  be  about  right  for  guarding  purposes.  Iron  seems  to  be  the  most 
desirable  material  for  guard  wires  because  it  gives  the  required  mechani- 
cal strength  and  sufficient  conductivity  at  a  less  cost  than  copper,  alumi- 
num, or  bronze,  and  is  easier  to  handle  and  less  liable  to  break  than  steel. 
It  was  formerly  the  practice  to  staple  guard  wires  to  the  tops  of  poles  or 
to  the  ends  of  cross-arms,  but  it  was  found  that  the  wire  was  more  apt 
to  rust  and  break  at  the  staple  than  elsewhere,  and  in  the  better  class  of 
work  such  wires  are  now  mounted  on  small  insulators.  This  practice, 
as  stated  above,  was  followed  on  the  Montreal  and  Chambly  line.  In 
all  cases  the  connection  between  the  guard  wire  and  each  of  its  ground 
wires  should  be  soldered,  and  the  ground  wire  should  have  a  large  sur- 
face in  contact  with  damp  earth,  either  through  a  soldered  joint  with  a 
ground  plate  by  winding  a  number  of  turns  about  the  butt  of  the  pole, 
or  bv  other  means. 

It  is  thought  by  some  telegraph  engineers  that  the  use  of  a  separate 
ground  wire  running  to  the  top  of  each  pole  is  quite  as  effective  as  a  pro- 
tection against  lightning  as  is  a  guard  wire  that  runs  to  all  of  the  poles 
and  is  frequently  connected  to  the  ground. 

This  practice  is  mentioned  at  page  26  of  "Culley's  Handbook  of 
Practical  Telegraphy."  Such  ground  wires  are  free  from  most  of  the 


176     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

objections  to  the  ordinary  guard  wires.  It  seems  quite  certain  that  a 
guard  wire  along  an  alternating-current  line,  and  grounded  at  frequent 
intervals,  must  act  as  a  secondary  circuit  of  a  transformer  by  reason  of 
its  ground  connections,  and  thus  absorb  some  energy  from  the  power 
circuits.  No  experimental  data  are  yet  available,  however,  to  show  how 
large  this  loss  may  be  in  an  ordinary  case.  It  is  fairly  evident  that  there 
must  be  some  electrostatic  effects  between  the  working  conductors  and 
a  guard  wire,  but  here  again  data  are  lacking  as  to  the  amount  of  any 
such  effect.  On  most,  if  not  all,  transmission  lines  the  guard  wire  or 
wires,  if  used  at  all,  are  placed  either  above  or  on  a  level  with  the  highest 
power  conductors.  With  one  conductor  of  a  three-phase  circuit  mounted 
on  a  pin  set  in  the  top  of  a  pole,  and  the  two  remaining  conductors  on  a 
two-pin  cross-arm  beneath,  in  the  method  most  frequently  adopted  for 
transmission  lines  of  very  high  voltage,  it  is  obviously  impracticable  to 
put  guard  wires  either  above  or  on  a  level  with  the  power  circuits.  In 
the  latest  transmissions  there  is  a  strong  tendency  to  omit  guard  wires  en- 
tirely and  rely  on  lightning  arresters  for  protection. 

Lightning  arresters  are  wrongfully  named,  for  their  true  purpose  is 
not  to  arrest  or  stop  lightning,  but  to  offer  it  so  easy  a  path  to  the  ground 
that  it  will  not  force  its  way  through  the  insulation  of  the  line  or  of  ma- 
chinery connected  to  the  system.  The  requirements  of  a  lightning  ar- 
rester are  in  a  degree  conflicting,  because  the  resistance  of  the  path  it 
offers  must  be  so  low  as  to  allow  discharges  of  atmospheric  electricity 
to  earth  and  so  high  as  to  prevent  any  flow  of  current  between  the  trans- 
mission lines.  In  other  words,  the  insulation  of  the  line  conductors  must 
be  maintained  at  a  high  standard  in  spite  of  the  connection  of  lightning 
arresters  between  each  conductor  and  the  earth;  but  the  resistance  to  the 
arrester  must  not  be  so  high  that  lightning  will  pierce  the  insulation  of 
the  line  or  machinery  at  some  other  point.  When  a  lightning  discharge 
takes  place  through  an  arrester  the  resistance  which  the  arrester,  offers 
to  a  flow  of  current  is  for  the  moment  greatly  reduced  by  the  arcs  which 
the  lightning  sets  up  in  jumping  the  air-gaps  of  the  arrester.  Each  wire 
of  a  transmission  circuit  must  be  connected  alike  to  arresters,  and  the 
paths  of  low  resistance  through  arcs  in  these  arresters  to  the  earth  would 
obviously  short-circuit  the  connected  generators  unless  some  construction 
were  adopted  to  prevent  this  result.  In  some  early  types  of  lightning 
arresters  magnetic  or  mechanical  devices  were  resorted  to  in  order  to 
break  arcs  formed  by  the  discharge  of  lightning. 

The  type  of  lightning  arrester  now  in  common  use  on  transmission 
lines  with  alternating  current  includes  a  row  of  short,  parallel,  brass 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      177 

cylinders  mounted  on  a  porcelain  block  and  with  air-gaps  of  one- 
thirty-second  to  one-sixteenth  of  an  inch  between  their  parallel  sides. 
The  cylinder  at  one  end  of  the  row  is  connected  to  a  line  wire  and  the 
cylinder  at  the  other  end  to  the  earth,  when  a  2,000  or  2, 500- volt  cir- 
cuit is  to  be  protected.  For  higher  voltages  a  number  of  these  single 
arresters  are  connected  in  series  with  each  other  and  with  the  free  ends 
of  the  series  to  a  line  wire  and  to  the  earth,  respectively.  Thus,  for 
a  1 0,000- volt  line,  four  or,  better,  five  single  arresters  are  connected  in 
series  to  form  a  composite  arrester  for  each  line  conductor.  For  any 
given  line  voltage  the  number  of  single  arresters  going  to  make  up  the 
composite  arrester  should  be  so  chosen  that  the  regular  working  voltage 
will  not  jump  the  series  of  air-gaps  between  the  little  brass  cylinders, 
but  yet  so  that  any  large  rise  of  voltage  will  be  sufficient  to  force  sparks 
across  these  gaps.  A  variation  of  this  practice  by  one  large  manufactur- 
ing company  is  to  mount  the  group  of  single  arresters  on  a  marble  board 
in  series  with  each  other  and  with  an  adjustable  air-gap.  This  gap  is 
intended  to  be  so  adjusted  that  any  large  increase  of  voltage  on  the  lines 
will  be  relieved  by  a  spark  discharge.  An  arrester  made  up  entirely 
of  the  brass  cylinders  and  air-gaps  has  the  disadvantage  that  an  arc 
once  started  between  all  the  cylinders  by  a  lightning  discharge  so  lowers 
the  resistance  between  each  line  wire  and  the  earth  that  the  generating 
equipment  is  short-circuited  and  the  arcs  may  not  cease  with  the  escape 
of  atmospheric  electricity.  To  avoid  this  difficulty  it  is  the  practice  to 
connect  a  conductor  of  rather  large  ohmic  resistance  such  as  a  rod  of 
carborundum  in  series  with  the  brass  cylinders  and  air-gaps  of  light- 
ning arresters.  This  resistance  should  be  non-inductive  so  as  not  to 
offer  a  serious  obstacle  to  lightning  discharge,  and  its  resistance  should 
be  great  enough  to  prevent  a  flow  of  current  from  the  generators  that 
will  be  large  enough  to  maintain  the  arcs  started  in  the  arrester  by  the 
lightning  discharge.  Accurate  data  are  lacking  as  to  the  amount  of 
this  resistance  that  should  be  employed  with  arresters  for  any  given 
voltage.  As  a  rough,  approximate  rule  it  may  be  said  that  in  some 
cases  good  results  will  be  obtained  with  a  resistance  in  ohms  in  series 
with  a  group  of  lightning  arresters  that  represents  one  per  cent  of  the 
numerical  value  of  the  line  voltage.  That  is,  fora  10,000- volt  line  the 
group  of  arresters  for  each  wire  may  be  connected  to  earth  through 
a  resistance  of,  say,  100  ohms,  so  that  if  the  generator  current  fol- 
lows the  arc  of  a  lightning  discharge  through  the  arresters  it  must  pass 
through  a  fixed  resistance  of  200  ohms  in  going  from  one  line  wire  to 
another.  This  rule  is  given  merely  as  an  illustration  of  the  resistance 

12 


i ;8     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

that  will  work  well  in  some  cases,  and  should  not  be  taken  to  have  a 
general  application.  If  the  resistance  connected  in  series  with  lightning 
arresters  is  high,  the  tendency  is  a  little  greater  for  lightning  to  go  to 
earth  at  some  point  in  the  apparatus  where  the  insulation  is  low.  If 
only  a  small  resistance  is  employed  to  connect  lightning  arresters  with 
the  earth,  the  danger  is  that  arcs  formed  by  lightning  discharges  will 
be  followed  and  maintained  by  the  dynamo  currents.  In  one  make  of 
lightning  arrester  the  row  of  little  brass  cylinders  is  connected  at  the 
ends  to  carbon  rods  which  form  a  resistance  for  the  purpose  just  men- 
tioned. Two  of  these  carbon  rods  are  contained  in  each  arrester  for 
2,000  or  2,500  volts,  and  the  resistance  of  each  rod  may  be  anywhere 
from  several  score  to  several  hundred  ohms  as  desired.  This  form  of 
arrester  may  be  connected  directly  from  line  to  earth  without  the  inter- 
vention of  any  outside  resistance,  since  the  carbon  rods  may  easily  be 
given  all  the  resistance  that  is  desirable. 

One  of  the  most  important  features  in  the  erection  of  a  lightning 
arrester  is  its  connection  to  earth.  If  this  connection  is  poor  it  may 
render  the  arrester  useless  so  far  as  protection  from  lightning  is  concerned. 
It  need  hardly  be  said  that  ground  connections  formed  by  driving  long 
iron  spikes  into  the  walls  of  buildings  or  into  dry  earth  are  of  slight  value 
as  far  as  protection  from  lightning  is  concerned.  A  good  ground  connec- 
tion for  lightning  arresters  may  be  formed  with  a  copper  or  galvanized 
iron  plate,  which  need  not  be  over  one-sixteenth  of  an  inch  thick,  but 
should  have  an  area  of,  say,  ten  to  twenty  square  feet.  This  plate  may 
be  conveniently  made  up  into  the  form  of  a  cylinder  and  should  have  a 
number  of  half-inch  holes  punched  in  a  row  down  one  side  into  which 
one  or  more  copper  wires  with  an  aggregate  area  equal  to  that  of  a  No. 
4  or  No.  2  wire,  B.  &  S.  gauge,  should  be  threaded  and  then  soldered. 
This  plate  or  cylinder  should  be  placed  deep  enough  in  the  ground  to 
insure  that  the  earth  about  it  will  be  constantly  moist,  and  the  connected 
copper  wire  should  extend  to  the  lightning  arresters.  It  is  a  good  plan 
to  surround  this  cylinder  with  a  layer  of  coke  or  charcoal. 

A  good  earth  connection  for  lightning  arresters  may  be  made  through 
large  water-pipes,  but  to  do  this  it  is  not  enough  simply  to  wrap  the  wire 
from  the  lightning  arresters  about  the  pipe.  A  suitable  contact  with 
such  a  pipe  may  be  made  by  tapping  one  or  two  large  bolts  into  it  and 
then  soldering  the  wires  from  lightning  arresters  into  holes  drilled  in  the 
heads  of  these  bolts.  A  metal  plate  laid  in  the  bed  of  a  stream  makes  a 
good  ground. 

With  some  of  the  older  types  of  lightning  arresters  it  was  the  custom 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      179 

to  insert  a  fuse  between  the  line  wire  and  the  ground,  but  this  practice 
defeats  the  purpose  for  which  the  arrester  is  erected  because  the  fuse 
melts  and  leaves  the  arrester  disconnected  and  the  circuit  unprotected 
with  the  first  lightning  discharge.  The  modern  arresters  for  alternating- 
current  circuits  are  made  up  of  a  series  of  metal  cylinders  and  short  air- 
gaps  and  are  connected  solidly  without  fuse  between  line  and  earth. 

It  was  once  the  practice  to  locate  lightning  arresters  almost  entirely 
in  the  stations,  but  this  has  been  modified  by  experience  and  considera- 


FIG.  73.— Entry  of  Lines  at  the  Power-house  on  Neversink  River. 


tion  of  the  fact  that  as  the  line  acts  as  a  collector  of  atmospheric  electric- 
ity, paths  for  its  escape  should  be  provided  along  the  line.  Consideration 
fails  to  reveal  any  good  reason  why  lightning  that  reaches  a  transmission 
line  some  miles  from  a  station  should  be  forced  to  travel  to  the  station, 
where  it  may  do  great  damage  before  it  finds  an  easy  path  to  earth.  It 
is,  therefore,  present  practice  to  connect  lightning  arresters  to  each  wire  at 
intervals  along  some  lines  as  well  as  at  stations  and  sub-stations.  The 
main  purpose  of  arresters  is  to  offer  so  easy  a  path  to  earth  that  lip-ht- 
ning  discharges  along  the  lines  will  not  flow  to  points  of  low  insulation 


iSo    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

in  generators,  transformers,  or  even  the  line  itself.  Practice  is  far  from 
uniform  as  to  the  distance  between  lightning  arresters  on  transmission 
lines,  the  distances  varying  from  less  than  one  to  a  large  number  of 
miles  apart.  In  general  the  lines  should  be  provided  with  lightning  ar- 
resters at  least  where  they  run  over  hilltops  and  at  any  points  where 
lightning  strokes  are  unusually  frequent.  Where  a  long  overhead 
line  joins  an  underground  cable  arresters  should  always  be  connected, 
and  the  same  is  true  as  to  transformers  located  on  the  transmission  line. 
The  multiplication  of  arresters  along  pole  lines  should  be  avoided  as  far 
as  is  consistent  with  suitable  protection,  because  every  bank  of  arresters 
may  develop  a  permanent  ground  or  short-circuit,  unless  frequently  in- 
spected and  kept  clean  and  in  good  condition. 

Arresters,  besides  those  connected  along  the  lines,  should  be  located 
either  in  or  just  outside  of  stations  and  sub-stations.  If  the  buildings 
are  of  wood,  the  arresters  had  better  be  outside  in  weather-proof  cases, 
but  in  brick  or  stone  buildings  the  arresters  may  be  properly  located 
near  an  interior  wall  and  well  removed  from  all  other  station  equipment. 
Transmission  lines,  on  entering  a  station  or  sub-station,  should  pass 
to  the  arresters  at  once  and  before  connecting  with  any  of  the  operating 
machinery. 

To  increase  the  degree  of  protection  afforded  by  lightning  arresters 
choke-coils  -are  frequently  used  with  them.  A  choke-coil  for  this  pur- 
pose usually  consists  of  a  flat  coil  of  copper  wire  or  strip  containing  twenty 
to  thirty  or  more  turns  and  mounted  with  terminals  in  a  wooden  frame. 
This  coil  is  connected  in  series  with  the  line  wire  between  the  point  where 
the  tap  for  the  lightning  arrester  is  made  and  the  station  apparatus. 
Lightning  discharges  are  known  to  be  of  a  highly  oscillatory  character, 
their  frequency  being  much  greater  than  that  of  the  alternating  currents 
developed  in  transmission  systems.  The  self-induction  of  a  lightning 
discharge  in  passing  through  one  of  these  choke-coils  is  great,  and  the 
consequent  tendency  is  to  keep  the  discharge  from  passing  through  the 
choke-coil  and  into  the  station  apparatus  and  thus  to  force  the  discharge 
to  pass  to  earth  through  the  lightning  arrester.  The  alternating  current 
employed  in  transmission  has  such  a  comparatively  low  frequency  that 
its  self-induction  in  a  choke-coil  is  small.  Increased  protection  against 
lightning  is  given  by  the  connection  of  several  groups  of  lightning  arrest- 
ers one  after  another  on  the  same  line  wire  at  an  electric  station.  This 
4 

gives  any  lightning  discharge  that  may  come  along  the  wire  several  paths 
to  earth  through  the  different  groups  of  arresters,  and  a  discharge  that 
passes  the  first  group  will  probably  go  to  earth  over  the  second  or  third 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      181 

group.  In  some  cases  a  choke-coil  is  connected  into  a  line  wire  between 
each  two  groups  of  lightning  arresters  as  well  as  between  the  station  ap- 
paratus and  the  group  of  arresters  nearest  thereto. 

An  electric  transmission  plant  at  Telluride,  Col,  where  thunder- 
storms are  very  frequent  and  severe,  was  equipped  with  arresters  and 
choke-coils  of  the  type  described,  and  the  results  were  carefully  noted 
(vol.  xi.,  A.  I.  E.  E.,  p.  346).  A  small  house  for  arresters  and  choke-coils 
was  built  close  to  the  generating  station  of  this  system  and  they  were 
mounted  therein  on  wooden  frames.  Four  choke-coils  were  connected 
in  series  with  each  line  wire,  and  between  these  choke-coils  three  lightning 
arresters  were  connected,  while  a  fourth  arrester  was  connected  to  the 
line  before  it  reached  any  of  the  choke-coils.  These  arresters  were 
watched  during  an  entire  lightning  season  to  see  which  bank  of  arrest- 
ers on  each  wire  discharged  the  most  lightning  to  earth.  It  was  found 
that,  beginning  on  the  side  that  the  line  came  to  the  series  of  arresters, 
the  first  bank  of  arresters  was  traversed  by  only  a  few  discharges  of 
lightning,  the  second  bank  by  more  discharges  than  any  other,  the 
third  bank  by  quite  a  large  number  of  discharges,  and  the  fourth  bank 
seldom  showed  any  sign  of  lightning  discharge.  Over  the  second 
bank  of  arresters  the  lightning  discharges  would  often  follow  each 
other  with  great  rapidity  and  loud  noise.  The  obvious  conclusion  from 
these  observations  seems  to  be  that  three  or  four  banks  of  lightning  arrest- 
ers connected  in  succession  on  a  line  at  a  station  together  with  choke-coils 
form  a  much  better  protection  from  lightning  than  a  single  bank.  At 
the  plant  in  question,  that  of  the  San  Miguel  Consolidated  Gold  Mining 
Company,  the  entire  lightning  season  after  the  erection  of  the  arresters 
in  question  was  passed  without  damage  by  lightning  to  any  of  the  equip- 
ment. During  the  two  lightning  seasons  previous  to  that  just  named 
the  damage  by  lightning  to  the  generating  machinery  at  the  plant  had 
been  frequent  and  extensive. 

A  good  illustration  of  the  high  degree  of  security  against  lightning 
discharges  that  may  be  attained  with  lightning  arresters  and  choke-coils 
exists  at  the  Niagara  Falls  plants  and  the  terminal  house  in  Buffalo, 
where  the  step-up  and  step-down  transformers  have  never  been  damaged 
by  lightning  though  the  transmission  line  has  been  struck  repeatedly  and 
poles  and  cross-arms  shattered  (vol.  xviii.,  A.  I.  E.  E.,  p.  527).  This  ex- 
ample bears  out  the  general  experience  that  lightning  arresters,  though 
not  an  absolute  protection,  afford  a  high  degree  of  security  to  the  appara- 
tus at  electric  stations. 

Lightning  arresters  are  in  some  cases  connected  across  high-voltage 


182     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

circuits  from  wire  to  wire  so  that  the  full  line  pressure  tends  to  force  a 
current  across  the  air-gaps.  The  object  of  this  practice  is  to  guard 
against  excessive  voltages  on  the  circuit  such  as  might  be  due  to  reso- 
nance. In  such  a  case,  as  in  that  where  arresters  are  connected  from 
line  wire  to  earth  as  a  protection  against  lightning,  the  number  of  air- 
gaps  should  be  such  that  the  normal  line  voltage  will  not  force  sparks 
across  the  air-gaps  and  thus  start  arcs  between  the  cylinders. 

The  number  and  total  length  of  air-gaps  in  a  bank  of  arresters 
necessary  to  prevent  the  formation  of  arcs  by  the  regular  line 
voltage  depends  on  a  number  of  factors  besides  the  amount  of  that 
voltage. 

According  to  the  report  of  the  Committee  on  Standardization  of  the 
American  Institute  of  Electrical  Engineers,  the  sparking  distances  in  air 
between  opposed  sharp  needle  points  for  various  effective  sinusoidal  volt- 
ages are  as  follows  (vol.  xix.,  A.  I.  E.  E.,  p.  1091) : 


Kilovolt  Square 
Root  of  Mean  Square. 

Inches  Sparking 
Distance. 

Kilovolt  Square 
Root  of  Mean  Square. 

Inches  Sparking 
Distance. 

5 

0.225 

60 

4-65 

10 

IS 

-47 
-725 

£ 

5-85 
7-1 

20 

I.O 

90 

8-35 

25 

i-3 

100 

9.6 

3° 

1.625 

no 

!°-75 

35 

2.O 

120 

11.85 

40 

2-45 

130 

12.95 

45 

2-95 

140 

13-95 

5° 

3-55 

!5° 

15.0 

It  may  be  noted  at  once  from  this  table  that  the  sparking  distance 
between  the  needle  points  increases  much  faster  than  the  voltage  between 
them.  Thus,  20,000  volts  will  jump  an  air-gap  of  only  an  inch  between 
the  points,  but  seven  times  this  pressure,  or  140,000  volts,  will  force  a 
spark  across  an  air-gap  of  13.95  inches.  Two  cylinders  or  other  blunt 
bodies  show  smaller  sparking  distances  between  them  at  a  given  voltage 
than  do  two  needle  points,  but  when  a  number  of  cylinders  are  placed 
in  a  row  with  short  air-gaps  between  them  the  aggregate  length  of  these 
gaps  that  will  just  prevent  the  passage  of  sparks  at  a  given  voltage 
may  be  materially  greater  or  less  than  the  sparking  distance  of  that 
voltage  between  needle  points.  It  has  been  found  by  experiment  that 
the  numbers  one-thirty-second-inch  spark-gaps  between  cylinders  of 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      183 

non-arcing  alloy  necessary  to  prevent  the  passage  of  sparks  with  the 
voltages  named  and  a  sine  wave  of  electromotive  force  are  as  follows 
(vol.  xix.,  A.  I.  E.  E.,  p.  1026): 


*^a 

1* 

O  O) 


-O 


5 

10 

15 

20 


6,800 
IO,OOO 
12,500 
14,500 


25 

3° 
35 
40 


16,400 
18,200 
19,300 
20,500 


45 
5° 

g 


21,700 
22,600 
23,900 
25,000 


65 

70 

75 
80 


26,000 
27,000 
28,000 
29,000 


According  to  these  data,  only  ten  air-gaps  of  one- thirty-second  of  an 
inch  each  and  0.3125  inch  combined  length  are  required  between  cylin- 
ders to  prevent  a  discharge  at  10,000  volts,  though  opposed  needle  points 
may  be  0.47  inch  apart  when  a  spark  is  obtained  with  this  voltage.  On 
the  other  hand,  eighty  air-gaps  of  one-thirty-second  of  an  inch  each  be- 
tween cylinders  of  non-arcing  metal,  or  a  total  gap  of  2.5  inches,  are 
necessary  to  prevent  a  discharge  at  29,000  volts,  though  30,000  volts  can 
force  a  spark  across  a  single  gap  of  only  1.625  inches  between  opposed 
needle  pgints. 

Under  the  conditions  that  existed  in  the  test  just  recorded  the  pressure 
at  which  the  aggregate  length  of  one-thirty-second  of  an  inch  air-gaps 
that  just  prevents  a  discharge  equals  the  single  sparking  distance  be- 
tween needle  points  seems  to  be  about  18,000  volts. 

The  object  of  dividing  the  total  air-gap  in  a  lightning  arrester  for 
lines  that  carry  alternating  current  up  into  a  number  of  short  gaps  is  to 
prevent  the  continuance  of  an  arc  by  the  regular  generator  or  line  current 
after  the  arc  has  been  started  by  a  lightning  discharge.  As  soon  as  an 
electric  spark  leaps  through  air  from  metal  to  metal,  a  path  of  low  elec- 
trical resistance  is  formed  by  the  intensely  heated  air  and  metallic  vapor. 
If  the  arc  thus  formed  is,  say,  two  inches  long  it  will  cool  a  certain  amount 
as  the  passing  current  grows  small  and  drops  to  zero.  If,  however,  this 
total  arc  of  two  inches  is  divided  into  sixty-four  parts  by  pieces  of  metal, 
the  process  of  cooling  as  the  current  decreases  will  go  on  much  more 
rapidly  than  with  the  single  arc  of  two  inches  because  of  the  great  con- 
ducting power  of  the  pieces  of  metal.  As  an  alternating  current  comes 
to  zero  twice  in  each  period,  the  many  short  arcs  formed  in  an  arrester 


184     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

by  a  lightning  discharge  are  so  far  cooled  during  the  small  values  of  the 
following  line  current  that  the  resistance  quickly  rises  to  a  point  where 
the  regular  line  voltage  cannot  continue  to  maintain  them,  if  the  arrester 
is  properly  designed  for  the  system  to  which  it  is  connected.  In  this 
way  the  many-gap  arrester  destroys  the  many  small  arcs  started  by  light- 
ning discharges  that  would  continue  and  short-circuit  the  line  if  they  were 
combined  into  a  single  long  arc. 

When  an  electric  arc  passes  between  certain  metals  like  iron  and 
copper  a  small  bead  is  raised  on  their  surfaces.  If  these  metals  were 
used  for  the  cylinders  of  arresters  the  beads  on  their  surface  would  quickly 
bridge  the  short  air-gaps.  Certain  other  metals,  like  zinc,  bismuth,  and 
antimony,  are  pitted  by  the  passage  of  arcs  between  their  surfaces.  By 
suitable  mixture  of  metals  from  these  two  classes,  an  alloy  is  obtained  for 
the  cylinders  of  lightning  arresters  that  pits  only  slightly  and  is  thus  but 
little  injured  by  lightning  discharges.  After  long  use  and  many  dis- 
charges an  arrester  of  the  class  here  considered  gradually  loses  its  power 
to  destroy  electric  arcs.  This  may  be  due  to  the  burning  out  of  the  zinc 
and  leaving  a  surface  of  copper  on  the  cylinders. 

Aside  from  the  structure  of  an  arrester  and  the  normal  voltage  of 
the  circuit  to  which  it  is  connected,  its  power  to  destroy  arcs  set  up  by 
lightning  discharges  depends  on  the  capacity  of  the  connected  genera- 
tors to  deliver  current  on  a  short-circuit  through  the  gaps,  and  upon  the 
inductance  of  the  circuit.  The  greater  the  capacity  of  the  generators 
connected  to  a  system  the  more  trying  are  the  conditions  under  which 
arresters  must  break  an  arc  because  the  current  to  be  broken  is  greater. 
So,  too,  an  increase  of  inductance  in  a  circuit  adds  to  the  work  of  an 
arrester  in  breaking  an  arc. 

An  arc  started  by  lightning  discharge  at  that  period  of  a  voltage  phase 
when  it  is  at  or  near  zero  is  easily  destroyed  by  the  arrester,  but  an  arc 
started  at  the  instant  when  the  regular  line  voltage  has  its  maximum 
value  is  much  harder  to  break  because  of  the  greater  amount  of  heat  gen- 
erated by  the  greater  current  sent  through  {he  arrester.  For  this  reason 
the  arcs  at  arresters  will  hold  on  longer  in  some  cases  than  in  others,  ac- 
cording to  the  portion  of  the  voltage  phase  in  which  they  are  started  by 
the  lightning  discharge.  Lightning  discharges,  of  course,  may  occur  at 
any  phase  of  the  line  voltage,  and  for  this  reason  a  number  of  discharges 
must  take  place  before  it  can  be  certain  from  observation  that  a  particular 
arrester  will  always  break  the  resulting  arc.  Between  twenty-five  and 
sixty  cycles  per  second  there  is  a  small  difference  in  favor  of  the  latter 
in  the  power  of  a  given  arrester  to  break  an  arc,  due  probably  to  the  fact 


GUARD  WIRES  AND  LIGHTNING  ARRESTERS.      185 

that  more  heat  in  the  arcs  is  developed  per  phase  with  the  lower  than  with 
the  higher  frequency. 

It  will  now  be  seen  that  while  increase  of  the  regular  line  voltage  re- 
quires a  lengthening  of  the  aggregate  air-gap  in  lightning  arresters  to 
prevent  the  formation  of  arcs  by  this  voltage  alone,  the  increase  of  gen- 
erating capacity  requires  more  subdivisions  of  the  total  air-gap  in  order 
that  the  arcs  maintained  by  the  larger  currents  may  be  cooled  with  suffi- 
cient rapidity.  These  two  requirements  are  to  some  extent  conflicting, 
because  the  subdivision  of  the  total  air-gaps  renders  it  less  effective  to 
prevent  discharges  due  to  the  normal  line  voltage,  as  has  already  been 
shown.  The  result  is  that  the  more  an  air-gap  is  subdivided  in  order  to 
cool  and  destroy  arcs  that  have  been  started  by  lightning,  the  longer  must 
be  the  aggregate  air-gap  in  order  to  prevent  the  development  of  arcs 
directly  by  the  normal  line  voltage. 

Furthermore,  'the  practical  limit  of  subdivision  of  the  air-gap  is  soon 
reached  because  of  the  difficulty  of  keeping  very  short  gaps  clean  and  of 
nearly  constant  length.  As  a  resistance  in  series  with  an  arrester  cuts 
down  the  generator  current  that  can  follow  a  lightning  discharge,  such 
a  resistance  also  decreases  the  number  of  air-gaps  necessary  to  give  an 
arrester  power  to  destroy  arcs  on  a  particular  circuit. 

The  increase  of  resistance  in  series  with  a  lightning  arrester  as  well  as 
the  increase  in  the  aggregate  length  of  its  air-gaps  subjects  the  insulation 
of  connected  apparatus  to  greater  strains  at  times  of  lightning  discharge. 
On  systems  of  large  capacity  the  number  and  aggregate  length  of  air- 
gaps  in  arresters  necessary  to  destroy  arcs  must  be  greater  than  the  num- 
ber or  length  of  these  air-gaps  necessary  to  prevent  the  development  of 
arcs  by  the  normal  line  voltage,  unless  a  relatively  large  resistance  is  con- 
nected in  series  with  each  arrester.  To  reduce  the  strains  produced  on 
the  insulation  of  line  and  connected  apparatus  under  these  conditions  by 
lightning  discharges,  a  resistance  is  connected  in  shunt  with  a  part  of  the 
air-gaps  in  one  make  of  lightning  arrester.  The  net  advantage  claimed 
for  this  type  of  arrester  is  that  a  lower  resistance  may  be  used  in  series 
with  all  the  air-gaps  than  would  otherwise  be  necessary.  One-half  of 
the  total  number  of  air-gaps  in  this  arrester  are  shunted  by  the  shunt 
resistance  and  the  series  and  shunt  resistance  are  in  series  with  each  other. 
Only  the  series  air-gaps  or  those  that  are  not  shunted  must  be  jumped 
in  the  first  instance  by  the  lightning  discharge,  which  thus  passes  to  earth 
through  these  air-gaps  and  the  shunt  and  series  resistance  in  series.  An 
arc  is  next  started  in  the  shunted  air-gaps,  and  this  arc  is  in  turn  destroyed 
because  the  shunt  weakens  the  current  in  these  gaps.  This  throws  the 


186    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

entire  current  of  the  arc  through  the  series  air-gaps  and  the  shunt  and 
series  resistance  all  in  series  with  each  other.  As  the  shunt  resistance  is 
comparatively  large,  the  current  maintaining  the  arc  in  the  series  air-gaps 
is  next  so  reduced  that  this  arc  is  broken.  Taking  the  claims  of  its 
makers  jusf  as  they  stand,  the  advantages  of  the  shunted  air-gaps  are 
not  very  clear.  The  series  air-gaps  alone  must  evidently  be  such  that 
the  normal  line  voltage  will  not  start  an  arc  over  them,  and  these  same 
series  gaps  must  be  able  to  break  the  arcs  of  line  current  flowing  through 
them  and  the  shunt  and  series  resistance  all  in  series.  Evidently  the 
greatest  strain  on  the  insulation  of  the  line  and  apparatus  occurs  at  the 
instant  when  the  lightning  discharge  takes  place  through  the  series  gaps 
and  the  shunt  and  series  resistances  all  in  series  with  each  other. 

Why  develop  subsequent  arcs  in  the  shunted  air-gaps?  Why  not 
throw  the  shunted  air-gaps  away  and  combine  the  shunt  and  series  re- 
sistances ? 


CHAPTER  XIV. 

ELECTRICAL  TRANSMISSION  UNDER  LAND  AND  WATER. 

ENERGY  transmitted  over  long  distances  must  sometimes  pass  through 
conductors  that  are  underground  or  beneath  water.  In  some  other  cases 
it  is  a  question  of  relative  advantages  merely,  whether  portions  of  a  trans- 
mission line  go  under  water  or  overhead.  Where  the  transmitted  energy 
must  enter  a  sub-station  in  the  heart  of  a  large  city,  it  not  infrequently 
must  go  by  way  of  underground  conductors  without  regard  to  the  voltage 
employed.  In  some  cities  the  transmission  lines  may  be  carried  over- 
head, provided  that  their  voltage  is  within  some  moderate  figure,  but  not 
otherwise.  Here  it  becomes  a  question  whether  transmission  lines  at 
high  voltage  shall  be  carried  underground,  or  whether  transforming  sta- 
tions shall  be  established  outside  of  the  restricted  area  and  then  low- 
pressure  lines  brought  into  the  business  section  overhead  or  underground, 
as  desired.  Where  a  transmission  line  must  cross  a  steam  railway  track 
it  may  be  required  to  be  underground,  whether  the  voltage  is  reduced 
or  not.  The  distance  across  a  body  of  water  in  the  path  of  a  transmission 
line  may  be  so  great  that  a  span  is  impossible  and  a  cable  under  the  water 
therefore  necessary.  Such  a  cable  may  work  at  the  regular  line  voltage, 
or  a  transformer  station  may  be  established  on  one  side  or  on  each  side 
of  the  body  of  water.  Even  where  it  is  possible  to  span  a  body  of  water 
with  a  transmission  line,  the  cost  of  the  span  and  of  its  supports  may  be 
so  great  that  a  submarine  cable  is  more  desirable.  A  moderate  increase 
in  the  length  of  a  transmission  line  in  order  to  avoid  the  use  of  a  sub- 
marine cable  is  almost  always  advisable,  but  where  rivers  are  in  the  path 
of  the  line  it  is  generally  impossible  to  avoid  crossing  them  either  over- 
head or  underneath.  Thus,  St.  Paul  could  only  be  reached  with  the 
2 5, ooo- volt  line  from  the  falls  on  Apple  River  by  crossing  the  St.  Croix 
River,  one-half  mile  wide,  on  the  way.  In  order  to  carry  out  the  40,000- 
volt  transmission  between  Colgate  and  Oakland,  the  Carquinez  Straits, 
which  intervened  with  nearly  a  mile  of  clear  water,  were  crossed.  Some- 
times, as  in  the  former  of  the  two  cases  just  named,  an  existing  bridge 
may  be  utilized  to  support  a  transmission  line,  but  more  frequently  the 
choice  lies  between  an  overhead  span  from  bank  to  bank  of  a  river  and  a 
submarine  cable  between  the  same  points. 

187 


i88    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

The  prime  advantage  of  an  overhead  line  at  high  voltage  is  its  com- 
paratively small  first  cost,  which  is  only  a  fraction  of  that  of  an  under- 
ground or  submarine  cable  in  the  great  majority  of  instances.  At  very 
high  voltages,  like  40,000  to  50,000  or  more,  the  overhead  line  must  also 
be  given  first  place  on  the  score  of  reliability,  since  the  lasting  qualities 
of  underground  and  submarine  cables  at  such  pressures  is  as  yet  an  un- 
known quantity.  On  the  other  hand,  at  voltages  in  which  cable  insula- 
tion has  been  shown  by  experience  to  be  thoroughly  effective,  under- 
ground or  submarine  cables  may  be  more  reliable  than  overhead  lines 
because  of  the  greater  freedom  from  mechanical  disturbances  which  these 
cables  enjoy. 

In  the  business  portion  of  many  cities  a  transmission  line  must  go 
underground,  whether  its  voltage  is  high  or  low.  Under  these  conditions, 
it  maybe  desired  either  to  transmit  energy  to  a  sub-station  for  distribution 
within  the  area  where  conductors  must  be  underground,  or  to  transmit 
energy  from  a  generating  station  there  located  to  outside  points.  If  the 
transmitted  energy  is  reduced  in  pressure  before  reaching  such  a  sub- 
station, a  transforming  station  must  be  provided,  and  this  will  allow  the 
underground  cables  to  operate  at  a  moderate  voltage.  For  such  a  case 
the  advantages  as  to  insulation  at  the  lower  voltage  should  be  compared 
with  the  additional  weight  of  conductors  in  the  cable  and  the  cost  of  the 
transforming  apparatus  and  station.  If  the  voltage  at  which  current  is 
delivered  from  the  transforming  station  does  not  correspond  with  the  re- 
quired voltage  of  distribution  at  the  sub-station,  the  necessary  equip- 
ment of  step-down  transformers  is  doubled  in  capacity  by  lowering  the 
voltage  of  the  transmitted  energy  where  it  passes  from  the  overhead  line 
to  the  underground  cables.  Conditions  of  just  this  sort  exist  at  Buffalo 
in  connection  with  the  delivery  of  energy  from  the  power-stations  at 
Niagara  Falls.  This  transmission  was  first  carried  out  at  1 1 ,000  volts, 
and  a  terminal  station  was  located  at  the  Buffalo  city  limits  where  the 
overhead  lines  joined  underground  cables  that  continued  the  transmis- 
sion at  the  same  voltage  to  several  sub-stations  in  different  parts  of  the 
city.  Later  the  voltage  of  the  overhead  transmission  line  was  raised  to 
22,000,  and  it  not  being  thought  advisable  to  subject  the  insulation  of 
the  underground  cables  to  this  higher  pressure,  transformers  were  in- 
stalled at  the  terminal  station  to  lower  the  line  voltage  to  1 1 ,000  for  the 
underground  cables.  As  the  sub-stations  in  this  case  also  have  trans- 
formers, there  are  two  kilowatts  of  capacity  in  step-down  transformers 
for  each  kilowatt  of  delivery  capacity  at  the  sub-stations. 

The  saving  effected  in  capacity  of  transformers  and  in  the  weight  of 


TRANSMISSION  UNDER  LAND  AND  WATER.       189 


cables  by  continuing  the  full  transmission  voltage  right  up  to  the  sub- 
stations whence  distribution  takes  place  furnishes  a  strong  motive  to 
work  underground  cables  at  the  pressure  of  the  overhead  transmission 
line  of  which  they  form  a  continuation.  Thus,  at  Hartford,  the  10,000- 


L 


volt  overhead  lines  that  bring  energy  from  water-power  stations  to  the 
outskirts  of  the  city  connect  directly  in  terminal  houses  there  with  under- 
ground cables  that  complete  the  transmission  to  the  sub-station  at  the 
full  line  voltage.  In  Springfield,  Mass.,  the  overhead  transmission  lines 
from  water-power  stations  connect  directly  with  underground  cables  at 


i go     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

a  distance  of  nearly  two  miles  from  the  sub-station,  and  these  cables  are 
thus  subject  to  the  full  line  pressure  of  6,000  volts.  The  overhead  line 
that  brings  energy  at  25,000  volts  from  Apple  River  falls  to  St.  Paul  ter- 
minates about  three  miles  from  the  sub-station  there,  and  the  transmis- 
sion is  completed  by  underground  cables  that  carry  current  at  the  25,000- 
volt  pressure. 

In  these  and  similar  cases  the  relative  advantages  of  underground 
cables  at  the  full  voltage  of  transmission  and  of  overhead  lines  at  a  much 
lower  pressure,  in  the  central  portions  of  cities,  must  be  compared. 
The  overhead  lines  at  moderate  voltage  will  no  doubt  cost  less  in 
almost  every  case  than  underground  cables  of  equal  length  and  at  the 
full  transmission  voltage. 

As  an  offset  to  the  lower  cost  of  overhead  city  lines  at  moderate  volt- 
age, where  they  are  permitted  by  local  regulations,  comes  the  increase  in 
weight  of  conductors  due  to  the  low  pressure  on  the  overhead  lines,  and 
also  the  cost  of  additional  transformer  capacity,  unless  the  lines  that 
complete  the  transmission  operate  at  the  voltage  of  distribution.  The 
1 0,000- volt  lines  that  transmit  energy  from  Great  Falls  to  Portland,  Me., 
terminate  in  two  transformer  houses  that  are  distant  about  0.5  mile  and 
2.5  miles,  respectively,  from  the  sub-station  there.  In  these  transformer 
houses  the  voltage  is  reduced  to  2,500,  and  the  transmission  is  then  con- 
tinued at  this  pressure  to  the  sub-station  whence  distribution  takes  place 
without  further  transformation. 

Where  a  river  or  other  body  of  water  must  be  crossed  by  a  transmis- 
sion line,  either  of  three  plans  may  be  followed.  The  overhead  line  may 
be  continued  as  such  across  the  water,  either  by  a  single  span  or  by  two 
or  more  spans  supported  by  one  or  more  piers  built  for  that  purpose  in 
the  water.  The  overhead  line  may  connect  directly  with  a  submarine 
cable,  this  cable  being  thus  exposed  to  the  full  voltage  of  the  transmis- 
sion. As  a  third  expedient,  a  submarine  cable  may  be  laid  and  connected 
with  step-down  transformers  on  one  bank  and  with  step-up  transformers 
on  the  other  bank  of  the  river  or  other  body  of  water  to  be  crossed.  The 
overhead  lines  connecting  with  these  transformers  can  obviously  be  oper- 
ated at  any  desired  voltage,  and  this  is  also  true  of  the  cable. 

Even  though  the  distance  across  a  body  of  water  is  not  so  great  that 
a  transmission  line  can  not  be  carried  over  it  in  a  single  span,  the  cost 
of  such  a  span  may  be  large.  A  case  in  point  is  that  of  the  Colgate 
and  Oakland  line,  where  it  crosses  the  Carquinez  Straits  by  a  span  of 
4,427  feet.  These  straits  are  about  3,200  feet  wide  where  the  transmis- 
sion line  crosses,  and  overhead  lines  were  required  to  be  not  less  than 


TRANSMISSION  UNDER  LAND  AND  WATER.      191 

200  feet  above  high  water  so  as  not  to  impede  navigation.  In  order  to 
gain  in  ground  elevation  and  thus  reduce  the  necessary  height  of  towers, 
two  points  4,427  feet  apart  on  opposite  sides  of  the  straits  were  selected 
for  their  location.  Under  these  circumstances  two  steel  towers,  one  sixty- 
five  feet  and  the  other  225  feet  high,  were  required  to  support  the  four 
steel  cables  that  act  as  conductors  across  the  straits.  To  take  the  strain 
of  these  four  cables,  each  with  a  clear  span  nearly  three  times  as  great  as 
that  of  the  Brooklyn  Bridge,  eight  anchors  with  housed  strain  insulators 
were  constructed,  four  on  the  land  side  of  each  tower.  On  each  of  these 
anchors  the  strain  is  said  to  be  24,000  pounds.  At  each  end  of  the  cables 
making  this  span  is  a  switch-house  where  either  of  the  two  three-phase 
transmission  lines  may  be  connected  to  any  three  of  the  four  steel  cables, 
thus  leaving  one  cable  free  for  repairs.  It  is  not  possible  to  state  here 
the  relative  cost  of  these  steel  towers  and  cables  in  comparison  with  that 
of  submarine  cables  for  the  same  work,  but  at  first  glance  the  question 
appears  to  be  an  open  one.  The  voltage  of  40,000,  at  which  this  trans- 
mission is  carried  out,  is  probably  higher  than  that  on  any  submarine 
cable  in  use,  but  it  is  possible  that  a  suitable  cable  can  be  operated  at 
this  voltage.  Whatever  the  limitations  of  voltage  as  applied  to  subma- 
rine cables,  it  would,  of  course,  have  been  practicable  to  use  step-up  and 
step-down  transformers  at  the  switch-houses  and  thus  operate  a  subma- 
rine cable  at  any  voltage  desired. 

In  another  case,  on  a  transmission  between  Portsmouth  and  Dover, 
N.  H.,  it  was  necessary  to  cross  an  arm  of  the  sea  on  a  line  4,811  feet 
long  with  a  three-phase  circuit  operating  at  13,500  volts.  It  was  decided 
to  avoid  the  use  of  either  a  great  span  or  of  raising  and  lowering  trans- 
formers at  this  crossing,  and  to  complete  the  line  through  a  submarine 
cable  operating  at  the  full  voltage  of  transmission.  To  this  end  a  brick 
terminal  house  six  by  eight  feet  inside,  and  with  an  elevation  of  thirteen 
feet  from  the  concrete  floor  to  the  tile  roof,  was  erected  on  each  bank  of 
the  bay  at  the  point  where  the  submarine  cable  came  out  of  the  water. 
The  lead-covered  cable  pierced  the  foundation  of  each  of  these  terminal 
houses  at  a  point  four  feet  below  the  floor  level  and  rose  thence  on  one 
wall  to  an  elevation  eleven  feet  above  the  floor  to  a  point  where  connec- 
tion was  made  with  the  ends  of  the  overhead  lines.  From  this  connection 
on  each  of  the  three  conductors  a  tap  was  carried  to  a  switch  and  series 
of  lightning  arresters.  A  single  lead-covered  cable  containing  three  con- 
ductors makes  connection  between  these  two  terminal  houses.  At  each 
end  of  this  cable  the  lead  sheath  joins  a  terminal  bell  one  foot  long  and 
2.5  inches  in  outside  diameter,  increasing  to  four  inches  at  the  end  where 


i92    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  three  conductors  pass  out.     This  terminal  bell  is  filled  nearly  to  the 
flaring  upper  end  with  an  insulating  compound. 

In  the  instance  just  named  it  is  possible  that  the  cost  of  the  subma- 
rine cable  was  less  than  would  have  been  the  outlay  for  shore  supports 
and  a  span  nearly  a  mile  long  across  this  body  of  water. 

Underground  and  submarine  cables  have  been  operated  at  voltages 
suitable  for  transmission  during  periods  sufficiently  long  to  demonstrate 
their  general  reliability.  The  Ferranti  underground  cables  between 
Deptf ord  and  London  have  regularly  carried  current  at  1 1 ,000  volts  since 
a  date  prior  to  1890.  During  about  five  years  cables  with  an  aggregate 
length  of  sixteen  miles  have  transmitted  power  from  St.  Anthony's  Falls 
to  Minneapolis.  At  Buffalo,  some  thirty  miles  of  rubber-insulated  cables 
have  been  in  use  for  underground  work  at  11,000  volts  since  1897,  and 
eighteen  miles  of  paper-insulated  cable  since  the  first  part  of  1901. 
These  examples  are  enough  to  show  that  transmission  through  under- 
ground cables  at  11,000  to  12,000  volts  is  entirely  practicable.  At  Read- 
ing, Pa.,  an  underground  cable  one  mile  long  has  carried  three-phase 
current  at  16,000  volts  for  the  Oley  Valley  Railway  since  some  time  in 
1902.  The  cables  in  the  transmission  from  Apple  River  to  St.  Paul, 
which  carry  three-phase  current  at  25,000  volts,  have  a  total  length  of 
three  miles,  and  have  been  in  use  since  1900.  This  voltage  of  25,000  is 
probably  the  highest  in  regular  use  on  any  underground  or  submarine 
cable  conveying  energy  for  light  or  power.  From  the  experience  thus 
far  gained  there  is  much  reason  to  think  that  the  voltages  applied  to 
underground  cables  may  be  very  materially  increased  before  a  prohibitive 
cost  of  insulation  is  reached. 

On  submarine  cables  the  voltage  of  13,000  in  the  Portsmouth  and 
Dover  transmission,  above  mentioned,  is  perhaps  as  great  as  any  in  use. 
It  does  not  appear,  however,  that  any  material  difference  exists,  as  to  the 
strain  on  its  insulation  at  a  given  voltage,  between  a  cable  when  laid  in 
an  underground  conduit  and  when  laid  under  water.  In  either  case  the 
entire  stress  of  the  voltage  employed  operates  on  the  insulation  between 
the  several  conductors  in  the  cable  and  between  each  conductor  and  the 
metallic  sheath.  Underground  conduits  have  little  or  no  value  as  in- 
sulators of  high  voltages,  because  it  is  practically  impossible  to  keep  them 
water-tight  and  prevent  absorption  or  condensation  of  moisture  therein. 
For  these  reasons  a  cable  that  gives  good  results  at  25,000  volts  in  an 
underground  conduit  should  be  available  for  use  at  an  equal  voltage  under 
water.  The  standard  structure  of  high-voltage  cables  for  either  under- 
ground or  submarine  work  includes  a  continuous  metallic  sheath  outside 


TRANSMISSION  UNDER  LAND  AND  WATER.       193 


i94    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

of  each  conductor  or  of  each  group  of  conductors  that  goes  to  make  up 
a  circuit.  As  most  transmissions  are  now  carried  out  with  three-phase 
current,  the  three  conductors  corresponding  to  a  three-phase  circuit  are 
usually  contained  in  a  single  cable  and  covered  by  a  single  sheath.  The 
cables  used  in  transmission  systems  at  Portsmouth,  Buffalo,  and  St.  Paul 
are  of  this  type.  If  single-phase  or  two-phase  current  is  transmitted,  each 
cable  should  contain  the  two  conductors  that  go  to  make  up  a  circuit. 
In  work  with  alternating  currents  the  use  of  only  one  conductor  per  cable 
should  be  avoided  because  of  the  loss  of  energy  that  results  from  the  cur- 
rents induced  in  the  metallic  sheath  of  such  a  cable. 

Where  the  two,  three,  or  more  conductors  that  form  a  complete  cir- 
cuit for  alternating  current  are  included  in  a  single  metallic  sheath,  the 
inductive  effects  of  currents  in  the  several  conductors  tend  to  neutral- 
ize each  other  and  the  waste  of  energy  in  the  sheath  is  in  large  part 
avoided.  To  neutralize  more  completely  the  tendency  to  local  currents 
in  their  metal  sheath,  the  several  insulated  conductors  of  an  alternating 
circuit  are  sometimes  twisted  together,  after  being  separately  insulated, 
before  the  sheath  is  put  on.  Distribution  of  power  at  Niagara  Falls 
was  at  first  carried  out  through  single-conductor,  lead-covered  cables 
with  two-phase  current  at  2,200  volts.  One  objection  to  this  plan 
was  the  loss  of  energy  by  induced  currents  in  the  lead  coverings  of  the 
cables.  It  was  later  decided  to  adopt  three-phase  distribution  at 
10,000  volts  for  points  distant  more  than  two  miles  from  the  power-sta- 
tion. Each  three-phase  circuit  for  this  purpose  was  made  up  of  three 
conductors  separately  insulated  and  then  covered  with  a  single  lead 
sheath,  so  as  to  avoid  losses  through  induced  currents  in  the  latter. 
Underground  and  submarine  cables  for  operation  at  high  voltages  are 
generally  covered  with  a  continuous  lead  sheath  and  sometimes  with  a 
spiral  layer  of  galvanized  iron  wire.  For  high- voltage  work  under- 
ground the  lead  covering  is  generally  preferred  without  iron  wire,  but 
in  submarine  work  coverings  of  both  sorts  are  employed.  The  lead 
sheath  of  a  cable  being  continuous  completely  protects  the  insulation 
from  contact  with  gases  or  liquids.  As  ducts  of  either  tile,  wood,  or  iron 
form  a  good  mechanical  protection  for  a  cable,  the  rather  small  strength 
of  a  lead  sheath  is  not  a  serious  objection  in  conduit  work.  Submarine 
cables,  on  the  other  hand,  depend  on  their  own  outer  coverings  for  me- 
chanical protection,  and  may  be  exposed  to  forces  that  would  rapidly  cut 
through  a  lead  sheath.  Cables  for  operation  under  water  should  usually 
be  covered,  therefore,  with  a  layer  of  galvanized  iron  wires  outside  of 
the  lead  sheath.  These  wires  are  laid  closely  about  the  cable  in  spiral 


TRANSMISSION  UNDER  LAND  AND  WATER.      195 

form  and  are  usually  between  0.12  and  0.25  inch  in  diameter  each,  de- 
pending on  the  size  of  the  cable  and  its  location. 

Underground  conduits  cannot  be  relied  on  to  exclude  moisture  and 
acids  of  the  soil  from  the  cables  which  they  contain,  and  either  of  these 
agents  may  lead  to  destructive  results.  If  cables  insulated  with  rubber, 
but  without  a  protecting  covering  outside  of  it,  are  laid  in  underground 
conduits,  the  rubber  is  apt  to  be  rapidly  destroyed  by  fluids  and  gases 
that  find  their  way  into  the  conduit.  If  a  plain  lead-covered  cable  is 
employed  the  acids  of  the  soil  attack  it,  and  if  stray  electric  currents  from 
an  electric  railway  find  the  lead  a  convenient  conductor  it  is  rapidly  eaten 
away  where  they  flow  out  of  it.  To  avoid  both  of  these  results  the  under- 
ground cable  should  have  a  lead  sheath,  and  this  sheath  may  be  protected 
by  an  outside  layer  of  hernp  or  jute  treated  with  asphaltum. 

Rubber,  paper,  and  cotton  are  extensively  used  as  insulation  for 
underground  and  submarine  cables,  but  the  three  are  not  usually 
employed  together.  As  a  rule,  the  insulation  is  applied  separately  to 
each  conductor,  and  then  an  additional  layer  of  insulation  may  be 
located  about  the  group  of  conductors  that  go  to  make  up  the  cable. 
Where  rubber  insulation  is  employed,  a  lead  sheath  may  or  may  not  be 
added,  but  where  insulation  depends  on  cotton  or  paper  the  outer  cover- 
ing of  lead  is  absolutely  necessary  to  keep  out  moisture.  The  radial 
thickness  of  insulation  on  each  conductor  and  of  that  about  the  group  of 
conductors  in  a  cable  should  vary  according  to  the  voltage  of  operation. 

Cables  employed  between  the  generating  and  sub-stations  of  the  Man- 
hattan Elevated  Railway,  to  distribute  three-phase  current  at  11,000 
volts,  are  of  the  three-conductor  type,  rubber  insulated,  lead  covered, 
and  laid  in  tile  conduits.  Each  cable  contains  three  No.  ooo  stranded 
conductors,  and  each  conductor  has  its  own  insulation  of  rubber.  Jute 
is  laid  on  to  give  the  group  of  conductors  an  outer  circular  form,  and  out- 
side of  the  group  a  layer  of  insulation  and  then  a  lead  sheath  is  placed. 
Outside  diameter  of  this  cable  is  nearly  three  inches,  and  the  weight  nine 
pounds  per  linear  foot. 

The  1 1 ,000- volt,  three-phase  current  from  Niagara  Falls  is  distributed 
from  the  terminal  house  to  seven  sub-stations  in  Buffalo  through  about 
30  miles  of  rubber-insulated  and  18  miles  of  paper-insulated,  three-con- 
ductor, lead-covered  cables,  all  in  tile  conduits.  In  each  cable  the  three 
No.  ooo  stranded  conductors  are  separately  insulated  and  then  twisted 
into  a  rope  with  jute  yarn  laid  in  to  give  an  even  round  surface  .for  the 
lead  sheath  to  rest  on.  A  part  of  the  rubber-insulated  cables  have  each 
conductor  covered  with  -^-inch  of  30  per  cent  pure  rubber  compound, 


196     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

and  the  remaining  rubber  cables  have  /y-inch  covering  on  each  conduc- 
tor of  40  per  cent  pure  rubber  compound.  The  paper-insulated  cable 
has  ^f -inch  of  paper  around  each  conductor,  and  also  another  £f -inch 
of  paper  covering  about  the  group  of  three  conductors  and  next  to  the 
lead  sheath.  In  outside  diameter  the  rubber-insulated  cable  is  2  J  inches, 
and  of  the  paper-insulated  cable  2$  inches,  the  radial  thickness  of  the 
lead  sheath  being  J-inch  in  each  case.  It  is  reported  that  the  cables 
insulated  with  ^-inch  of  the  mixture,  said  to  be  30  per  cent  pure  rubber, 
have  proved  to  be  more  reliable  than  the  cables  insulated  with  -^-inch 
of  a  mixture  said  to  be  40  per  cent  pure  rubber.  Vol.  xviii.,  A.  I,  E.  E., 
136,  836. 

The  six  miles  of  underground  cables  that  carry  three-phase,  25,000- 
volt  current  in  St.  Paul  are  of  the  three-conductor  type,  lead  covered,  and 
laid  in  a  tile  conduit.  One  of  the  two  three-mile  cables  is  insulated  with 
rubber  and  the  other  with  paper.  In  the  former  cable  each  conductor 
is  separately  insulated  with  a  compound  containing  about  35  per  cent  of 
pure  rubber  and  having  a  radial  thickness  of  TVmcn-  The  three  con- 
ductors after  being  insulated  are  laid  up  with  jute  to  give  a  round  surface, 
tape  being  used  to  hold  them  together,  and  then  a  rubber  cover  -^--inch 
thick  is  placed  about  the  group,  after  which  comes  the  lead  sheath  over 
all.  In  the  three  miles  of  paper-insulated  cable  each  conductor  is  sep- 
arately covered  with  paper  to  a  thickness  of  -g^-inch,  then  the  three  con- 
ductors are  laid  together  with  jute  and  taped,  and  next  a  layer  of  paper 
-jVmcn  thick  is  put  on  over  the  group.  Outside  of  all  comes  the  lead 
sheath,  which  has  an  outer  coating  of  tin.  The  paper  insulation  in  these 
cables  was  saturated  with  a  secret  insulating  compound.  The  lead 
sheath  on  both  the  rubber  and  paper  insulated  cables  is  J-inch  thick  and 
the  sheath  of  the  former  contains  3  per  cent  of  tin.  Each  of  the  three 
conductors  in  each  cable  consists  of  7  copper  strands  and  has  an  area  of 
66,000  circular  mils.  Outside  of  the  lead  sheath  each  of  these  cables 
has  a  diameter  of  about  2  J  inches.  By  the  manufacturer's  contract  these 
cables  were  tested  up  to  40,000  volts  before  shipment,  and  might  be  tested 
up  to  30,000  volts  in  their  conduits  during  any  time  within  five  years  from 
their  purchase.  In  first  cost  the  cable  with  rubber  insulation  was  said 
to  be  about  50  per  cent  more  expensive  than  the  cable  in  which  paper  was 
used.  Vol.  xvii.,  A.  I.  E.  E.,  650. 

Underground  cables  in  which  the  separate  conductors  are  covered 
with  cotton  braid  treated  with  an  insulating  compound,  and  then  the 
group  of  conductors  going  to  make  up  the  cable  enclosed  in  a  lead  sheath, 
are  extensively  used  in  Austria  and  Germany.  For  cables  that  operate 


TRANSMISSION  UNDER  LAND  AND  WATER.      197 

at  10,000  to  12,000  volts  the  radial  thickness  of  cotton  insulation  on  each 
conductor  is  said  to  be  within  T3-g-inch,  and  these  cables  are  tested  up  to 
25,000  volts  by  placing  all  of  the  cable  except  its  ends  in  water,  and  then 
connecting  one  end  of  the  2 5,000- volt  circuit  to  the  water  and  the  other 
end  to  the  conductors  of  the  cable. 

A  test  on  the  paper-insulated  cable  at  St.  Paul  showed  its  charging 
current  to  be  i  .1  amperes  at  25,000  volts  for  each  mile  of  its  length.  For 
the  cable  with  rubber  insulation  the  charging  current  per  mile  of  length 
was  found  to  be  about  twice  as  great  as  the  like  current  for  the  paper- 
insulated  cable.  Each  of  the  two  overhead  transmission  lines  connected 
with  these  cables  consisted  of  three  solid  copper  wires  with  an  area  of 
66,000  circular  mils  each,  and  all  three  so  mounted  on  the  poles  as  to  form 
the  corners  of  an  equilateral  triangle  twenty-four  inches  apart.  The 
charging  current  of  one  of  these  three-wire,  overhead  circuits  was  found 
to  be  about  0.103  ampere  per  mile,  at  25,000  volts,  or  a  little  less  than 
one-tenth  of  the  like  current  for  the  paper  cable.  These  tests  were  made 
with  three-phase  current  of  sixty  cycles  per  second. 

Where  overhead  transmission  lines  join  underground  or  submarine 
cables,  either  with  or  without  the  intervention  of  transformers,  lightning 
arresters  should  be  provided  to  intercept  discharges  of  this  sort  that  come 
over  the  overhead  wires.  Lightning  arresters  were  provided  in  the  ter- 
minal house  at  Buffalo,  where  the  2 2,000- volt  overhead  lines  feed  the 
1 1, ooo- volt  cables  through  transformers,  also  at  the  terminal  house  in 
St.  Paul,  where  the  2 5, ooo- volt  overhead  lines  are  electrically  connected 
to  the  underground  cables.  If  an  underground  or  submarine  cable  con- 
nects two  portions  of  an  overhead  line,  as  in  the  Portsmouth  and  Dover 
transmission  above  mentioned,  lightning  arresters  should  be  provided  at 
each  end  of  the  cable,  as  was  done  in  that  case.  One  advantage  of  a 
high  rather  than  a  low  voltage  on  underground  cables,  where  power  is 
to  be  transmitted  at  any  given  rate,  lies  in  the  fact  that  the  amperes  flow- 
ing at  a  fault  in  the  cable  determine  the  destructive  effect  there,  rather 
than  the  voltage  of  the  transmission.  It  is  reported  that  a  fault  or  short- 
circuit  in  one  of  the  n, ooo- volt  cables  at  Buffalo  usually  melts  off  but 
little  lead  at  the  sheath  and  does  not  have  enough  explosive  force  to 
injure  the  cable  or  its  duct. 

Ozone  seems  to  destroy  the  insulating  properties  of  rubber  very  rap- 
idly, and  as  it  is  well  known  that  the  silent  electric  discharge  from  con- 
ductors at  high  voltages  develops  ozone,  care  should  be  taken  to  protect 
rubber  insulation  from  its  action.  This  is  especially  true  at  the  ends  of 
cables  where  connections  are  made  with  switches  or  other  apparatus,  and 


198     ELECTRIC < TRANSMISSION  OF  WATER-POWER. 

the  rubber  insulation  is  exposed.  To  protect  the  rubber  at  such  points 
it  is  the  practice  to  solder  a  brass  cable  head  or  terminal  bell  to  the  lead 
sheath  near  its  end,  this  head  having  a  diameter  perhaps  twice  as  great 
as  that  of  the  sheath,  and  then  to  fill  the  space  about  the  cable  conductors 
in  this  head  with  an  insulating  compound.  Heads  of  this  sort  were  used 
on  the  1 1, ooo- volt  cables  at  Buffalo  as  well  as  on  the  13, 500- volt  cable  in 
the  Portsmouth  and  Dover  transmission. 

As  insulating  materials,  whether  rubber,  cotton,  or  paper,  may  be 
impaired  or  destroyed  by  heat,  it  is  necessary  that  the  temperature  of 
underground  cables  under  full  load  be  kept  within  safe  limits.  Rubber 
insulation  can  probably  be  raised  to  125°  or  150°  Fahrenheit  without 
injury,  and  paper  and  cotton  may  go  a  little  higher.  For  a  given  size 
and  make  of  leaded  cable  the  rise  of  temperature  in  its  conductors  above 
that  of  the  surrounding  air,  for  a  given  loss  in  watts  per  foot  of  the  cable, 
may  be  determined  by  computation  or  experiment.  The  next  step  is  to 
find  out  how  much  the  temperature  of  the  air  in  the  conduits  where  the 
cable  is  to  be  used  will  rise  above  the  temperature  of  the  earth  in  which 
the  conduits  are  laid,  with  the  given  watt  loss  per  foot  of  cable.  On  this 
point  there  are  but  little  experimental  data.  Obviously,  the  material  of 
which  ducts  are  made,  the  number  of  ducts  grouped  together  with  cables 
operating  at  the  same  time,  and  the  extent  to  which  ducts  are  ventilated 
must  have  an  important  bearing  on  this  question.  At  Niagara  Falls 
some  tests  were  made  to  show  the  rise  of  air  temperature  in  a  section  of 
thirty-six-duct  conduit  lying  between  two  manholes  about  140  feet  apart. 
For  the  purpose  of  this  test  twenty-four  of  the  thirty-six  ducts  in  the  con- 
duit had  one  No.  6  drawing-in  wire  passed  through  each  of  them.  These 
twenty-four  wires  were  connected  into  three  groups  of  eight  wires  each, 
so  that  one  group  was  all  in  ducts  next  to  the  surrounding  earth,  another 
group  was  one-half  in  ducts  next  to  the  earth  and  the  other  half  in  ducts 
separated  from  the  earth  by  at  least  one  duct,  while  the  third  group  of 
wires  was  entirely  in  ducts  separated  from  the  earth  by  at  least  one  duct. 
It  was  found  that  when  enough  current  was  sent  through  these  wires  to 
represent  a  loss  of  5.5  watts  per  foot  of  ducts  in  which  they  were  located, 
the  rise  of  temperature  in  the  air  of  the  ducts  next  to  the  earth  was  about 
1 08°  Fahrenheit  above  that  of  the  earth.  For  the  ducts  separated  from 
the  earth  by  at  least  one  other  duct  the  rise  in  temperature  of  contained 
air  was  144°  Fahrenheit  above  the  earth.  If  the  earth  about  the  ducts 
reached  70°  in  hot  weather,  the  temperature  of  air  in  the  inner 
ducts,  with  a  loss  of  5.5  watts  per  duct  foot,  would  thus  be  214°. 
This  temperature  is  too  high  for  either  rubber,  cotton,  or  paper  insula- 


TRANSMISSION  UNDER  LAND  AND  WATER.      199 

tion,  to  say  nothing  of  the  amount  by  which  the  temperature  of  the  con- 
ductors and  insulation  of  a  cable  in  operation  must  exceed  that  of  the 
surrounding  air  in  its  duct.  The  cables  actually  installed  in  the  ducts 
just  considered  were  designed  for  a  loss  of  2.34  watts  per  foot.  As  the 
No.  6  wire  used  in  the  test  did  not  nearly  fill  each  duct  as  a  cable  would 
do,  it  would  be  very  interesting  to  know  how  much  ventilation  took  place 
while  the  test  was  going  on.  Unfortunately,  this  point  was  not  reported. 
Vol.  xviii.,  A.  I.  E.  E.,  508. 


CHAPTER  XV. 

MATERIALS  FOR  LINE  CONDUCTORS. 

COPPER,  aluminum,  iron,  and  bronze  are  all  used  for  conductors  in 
long-distance  electric  transmissions,  but  copper  is  the  standard  metal  for 
the  purpose.  An  ideal  conductor  for  transmission  lines  should  combine 
the  best  electrical  conductivity,  great  tensile  strength,  a  high  melting 
point,  low  coefficient  of  expansion,  hardness,  and  great  resistance  to  oxi- 
dation. No  one  of  the  metals  named  possesses  all  of  these  properties  in 
the  highest  degree,  and  the  problem  is  to  select  the  material  best  suited 
to  each  case.  Aluminum  suffers  very  slightly  by  exposure  to  the  weather, 
copper  and  bronze  suffer  a  little  more,  while  iron  and  steel  wire  are  at- 
tacked seriously  by  rust. 

Iron,  copper,  and  bronze  are  all  so  hard  that  little  or  no  trouble  has 
occurred  from  wires  of  these  metals  cutting  or  wearing  away  at  the  points 
of  attachment  to  insulators.  Aluminum,  on  the  other  hand,  is  so  soft 
that  swaying  of  the  wire  may,  in  time,  cause  material  wear  at  the  supports, 
or  it  may  be  cut  by  tie  wires.  But  lines  of  aluminum  wire  have  not  been 
in  use  long  enough  to  determine  how  much  trouble  is  to  be  expected  from 
its  lack  of  hardness. 

A  small  coefficient  of  expansion  is  desirable  in  transmission  wires, 
because  the  strain  on  the  wire  itself  and  on  its  supports  varies  rapidly 
with  the  amount  of  vertical  deflection  of  each  span,  becoming  greater  as 
the  deflection  decreases.  Taking  the  expansion  of  copper  as  unity, 
that  of  aluminum  is  1.4;  of  bronze,  i.i;  and  of  iron  and  steel,  0.7. 
From  these  figures  it  follows  that  iron  and  steel  wires  show  the  least 
variation  in  the  amount  of  sag  between  supports,  and  aluminum  wire 
shows  the  most. 

Wrought  iron  melts  at  about  2,800°,  steel  at  2,700°,  copper  at  1,929°, 
bronze  at  about  the  same  point  as  copper,  and  aluminum  at  1,157°  Fahr- 
enheit. This  low  melting  point  of  aluminum  may  prove  a  source  of 
trouble  by  opening  a  line  of  that  material  where  some  foreign  wire  falls 
on  it.  This,  according  to  a  report,  was  illustrated  at  a  sub-station  on  a 
30,ooo-volt  transmission  line  where  a  destructive  arc  was  started  at  the 
switchboard.  Not  being  able  to  extinguish  the  arc  in  any  other  way,  a 


MATERIALS  FOR  LINE  CONDUCTORS.  201 

lineman  threw  an  iron  wire  across  the  aluminum  lines  just  outside  of  the 
sub-station,  and  these  lines  were  immediately  melted  through  by  the  iron 
wire,  thus  opening  the  circuit.  The  trouble  may  have  warranted  so  des- 
perate a  remedy  in  this  case ;  but,  as  a  rule,  it  does  not  pay  to  cut  a  trans- 
mission line  in  order  to  get  rid  of  a  short  circuit. 

In  the  ordinary  construction  of  transmission  lines  on  land  the  tensile 
strength  of  wire  is  secondary  in  importance  to  its  electrical  conductivity, 
because  supports  can  be  spaced  according  to  the  strength  of  the  conductor' 
used.  When  large  bodies  of  water  must  be  crossed,  tensile  strength  is  a 
prime  requirement.  Thus  a  142-mile  line  from  Colgate  to  Oakland,  in 
California,  crosses  the  Straits  of  Carquinez  in  the  form  of  steel  cables, 
each  seven-eighths  of  an  inch  in  diameter  and  4,427  feet  long.  Steel  wire 
was  selected  for  this  long  span,  probably  because  it  can  be  given  a  greater 
tensile  strength  than  that  of  any  other  metal.  Annealed  iron  wire  has  a 
tensile  strength  between  50,000  and  60,000  pounds  per  square  inch. 
Steel  wires  vary  all  the  way  from  50,000  to  more  than  350,000  pounds  per 
square  inch  in  strength,  but  mild  steel  wire  with  a  strength  ranging  from 
80,000  to  100,000  pounds  per  square  inch  is  readily  obtained. 

Soft  copper  shows  a  tensile  strength  between  32,000  and  36,000 
pounds  per  square  inch,  and  hard-drawn  copper  between  45,000  and 
70,000  pounds,  depending  on  the  degree  of  hardness.  Silicon-bronze 
wires  vary  in  strength  from  less  than  60,000  to  more  than  100,000  pounds 
per  square  inch,  and  phosphor-bronze  has  a  tensile  strength  of  about 
100,000  pounds.  Bronze  wires,  like  those  of  most  alloys,  show  a  much 
wider  range  of  strength  than  those  of  iron  or  copper. 

In  silicon-bronze  wire  the  electrical  conductivity  decreases  as  "the 
tensile  strength  increases.  The  tensile  strength  of  aluminum  wire  is 
lower  than  that  of  any  other  used  in  transmission  lines,  being  only  about 
30,000  pounds  per  square  inch.  Solid  aluminum  wires  of  large  size  have 
given  trouble  by  breaking  under  strains  well  within  their  nominal 
strength,  due  probably. to  imperfections  or  twists.  This  trouble  is  now 
generally  avoided  by  the  use  of  aluminum  cables. 

In  that  most  necessary  property  of  a  transmission  line — conductivity 
— copper  excels  all  other  metals  except  silver.  Taking  the  conductivity 
of  soft  copper  wire  at  100,  the  conductivity  of  hard-drawn  copper  is  98; 
that  of  silicon-bronze  ranges  from  46  to  98;  that  of  aluminum  is  60;  of 
phosphor-bronze,  26;  of  annealed  iron  wire,  14;  and  of  steel  wire  of 
100,000  pounds  tensile  strength  per  square  inch,  n.  Copper  wire,  both 
soft  and  hard,  as  regularly  made,  does  not  vary  more  than  one  per  cent 
from  the  standard,  and  aluminum  and  annealed  iron  wires  also  show 


202     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

high  uniformity  as  to  resistance.  Silicon-bronze  and  steel  wires,  on  the 
other  hand,  fluctuate  much  in  electrical  conductivity.  For  any  particular 
transmission  line  the  resistance  is  usually  determined  by  considerations 
apart  from  the  metal  to  be  used  as  a  conductor,  so  that  a  line  of  given 
resistance  or  conductivity  must  be  constructed  of  that  material  which  best 
conforms  to  the  requirements  as  to  size  of  wire,  weight,  strength,  and 
cost. 

Allowing  the  weight  of  any  definite  mass  of  copper  to  represent  unity, 
the  weight  of  an  equal  mass  of  wrought  iron  is  0.87 ;  of  steel,  0.89 ;  of 
aluminum,  0.30;  while  that  of  bronze  is  very  nearly  equal  to  that  of  the 
copper.  The  smallest  line  wire  that  can  be  used  for  a  given  length  and 
resistance  is  one  of  pure,  soft  copper.  Next  in  cross-sectional  area  come 
hard-drawn  copper  and  some  silicon-bronze,  either  of  which  need  be 
only  two  per  cent  larger  than  the  soft  copper  for  an  equal  resistance. 
Some  other  silicon-bronze  wire  of  greater  tensile  strength  per  square  inch 
would  require  a  sectional  area  of  2.17  times  that  of  the  soft  copper. 

Aluminum  wire  with  60  per  cent  of  the  conductivity  of  copper  re- 
quires 1.66  of  its  section  for  wires  of  equal  resistance.  As  phosphor- 
bronze  has  only  26  per  cent  of  the  conductivity  of  copper,  the  section  of 
the  bronze  must  be  3.84  times  that  of  the  copper  wire  if  their  lengths  and 
resistance  are  to  be  equal.  An  annealed  iron  wire  is  equal  in  resistance 
to  a  copper  wire  of  the  same  length  when  the  iron  has  7.14  times  the  sec- 
tion of  the  copper.  Steel,  with  1 1  per  cent  of  the  conductivity  of  copper, 
must  have  9.09  times  the  copper  section  in  order  that  wires  of  the  same 
length  may  have  equal  resistances. 

It  is  not  desirable  to  use  a  copper  wire  smaller  than  No.  4  B.  &  S. 
gauge  for  transmission  lines,  because  of  the  lack  of  tensile  strength  in 
smaller  sizes.  When  the  conductivity  of  a  copper  wire  smaller  than  No. 
4  is  ample,  an  iron  wire  will  give  the  required  conductivity,  with  a  strength 
far  greater  than  that  of  the  copper.  For  a  line  of  given  length  and  con- 
ductivity of  any  other  metal  the  weight  compared  with  that  of  a  copper 
line  is  represented  by  the  product  of  the  figures  for  relative  section  of 
the  two  lines  and  of  the  weight  of  unit  mass  of  the  metal  in  question  com- 
pared with  that  of  copper. 

Thus,  for  the  same  conductivity  the  weight  of  a  certain  length  of  iron 
wire  is  0.87  x  7-J4  =  6-21  times  the  weight  of  a  copper  wire.  For  the 
steel  wire  above  named  the  weight  is  0.89  x  9-°9  =  8.09  times  that  of 
a  copper  line  of  equal  conductivity.  Phosphor-bronze  in  a  line  of  given 
length  and  resistance  has  3.84  times  the  weight  of  soft  copper.  Silicon- 
bronze  for  a  transmission  line  must  weigh  from  1.02  to  2.17  times  as 


MATERIALS  FOR  LINE  CONDUCTORS.  203 

much  as  soft  copper  for  a  given  length  and  conductivity.  Aluminum 
for  a  line  of  fixed  length  and  conductivity  will  weigh  1.66  x  0.3  =  0.5 
times  as  much  as  copper.  For  a  line  of  fixed  length  and  resistance, 
hard-drawn  copper  will  weigh  about  two  per  cent  more  than  soft 
copper. 

Taking  the  tensile  strength  of  soft  copper  at  34,000  pounds  per  square 
inch,  hard-drawn  copper  at  45,000  to  70,000,  silicon-bronze  at  60,000  to 
1 00,000,  phosphor-bronze  at  100,000,  iron  at  55,000,  steel  at  100,000,  and 
aluminum  at  30,000  pounds,  the  relative  strengths  of  wires  with  equal 
sectional  areas  compared  with  the  soft  copper  are,  for  hard-drawn  cop- 
per, 1.32  to  2.06;  silicon-bronze,  1.76  to  2.94;  phosphor-bronze,  2.94; 
iron,  1.62;  steel,  2.94;  and  for  aluminum,  0.88. 

Comparing  wires  on  the  basis  of  equal  resistances  for  equal  lengths, 
with  soft  copper  again  the  standard,  the  tensile  strength  of  each  as  to  it 
is  as  follows:  A  hard-drawn  copper  line  has  1.02  x  1-32  =  1.34  to 
i. 02  x  2.06  =  2.10  times  the  strength  of  a  line  of  soft  copper.  With 
silicon-bronze  the  strength  of  line  wire  would  range  between  1.02  x 
1.76  =  1.79  and  2.17  x  2.94  =  6.38  times  that  of  copper.  Iron  would 
give  the  line  a  strength  as  to  soft  copper  represented  by  7.14  x  1.62  = 
11.56.  Steel  of  100,000  pounds  tensile  strength  per  square  inch  will 
give  a  line  9.09  x  2.94  =  26.70  times  as  strong  as  it  would  be  if  com- 
posed of  soft  copper.  With  aluminum  the  strength  of  the  line  would  be 
1.66  x  0.88  =  1.46  times  that  of  copper.  For  phosphor-bronze  the  fig- 
ures are  3.84  x  2.94  =  11.29. 

From  the  foregoing  it  may  be  shown  how  many  times  the  price  of 
soft  copper  per  pound  may  be  paid  for  each  of  the  other  metals  to  form 
a  line  of  given  length  and  resistance  at  a  cost  equal  to  that  of  a  soft  cop- 
per line.  These  prices  per  pound  for  the  several  metals  relative  to  that 
of  soft  copper  are  as  follows:  Taking  the  price  of  soft  copper  as  one,  the 
price  for  hard-drawn  copper  must  be  i  -4-  1.02  =  0.98.  For  silicon- 
bronze  the  price  may  be  as  high  as  i  -f-  1.02  —  0.98,  or  as  low  as  i  -~ 
2.17  =  0.46  of  the  price  of  soft  copper  wire.  Phosphor-bronze  may 
have  a  price  represented  by  only  i  -f.  3.84  —  0.26  that  of  copper.  The 
price  of  iron  wire  should  be  i  -=-  6.21  =  0.16  of  that  of  copper,  and  for 
steel  wire  of  the  quality  stated  the  price  can  only  be  i  -j-  8.01  =  0.12. 
Aluminum  wire  alone  may  have  a  higher  price  per  pound  than  soft  cop- 
per for  the  same  resistance  and  cost  of  line,  the  figure  for  the  relative 
cost  of  this  metal  being  i  -j-  0.5  =  2. 

From  the  foregoing  it  appears  that  for  a  line  of  given  cost,  length, 
and  resistance,  soft  copper  has  the  least  cross-section  and  tensile  strength; 


204     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


steel,  the  greatest  cross-section,  weight,  tensile  strength,  and  lowest  per- 
missible price  per  pound ;  and  aluminum,  the  least  weight  and  highest 
price  per  pound. 

RELATIVE  PROPERTIES  OF  WIRES  HAVING  EQUAL  LENGTHS  AND  RESISTANCES. 


Metal  in  Wire. 

Relative 
Cross 
Sections. 

Relative 
Weights. 

Relative 
Tensile 
Strengths. 

<U  OJ  0.2 

.£&~r°  • 
tj  t/)T3r-i~ 
£  v  c  a)  o 
<u  H  3  c(j 

«£lj 

Soft  Copper  

I.OO 

I.OO 

I 

I  OO 

Hard  Copper  . 

I  02 

na 

Very  Hard  Copper  .  .  . 

I  02 

i  02 

i-v)4 

.90 
nc 

No.  i  Silicon-Bronze  .  .. 

I  02 

i  02 

.90 
08 

No.  2  Silicon-Bronze  

217 

2  17 

1.79 

6  ?8 

.90 
46 

i  66 

CQ 

i  46 

3.84 

3  8d 

1  1  2Q 

26 

Annealed  Iron 

7  id. 

£ 

rfi 

Mild  Steel. 

o  oo 

8  oo 

26  7O 

The  relative  cross  sections  and  weights  of  both  iron  and  steel  wires 
are  so  great  as  to  prevent  their  general  use  because  of  the  labor  and  cost 
of  their  erection. 

So  far  as  the  first  cost  of  the  wire  alone  is  concerned,  iron  may  be 
approximately  equal  to  copper  in  some  metal  markets.  The  only  prac- 
tical place  for  an  iron  wire,  however,  is  one  where  copper  would  be  too 
small  or  not  strong  enough.  Steel  wire  finds  a  place,  in  spite  of  its  high 
resistance,  in  those  exceptional  cases  where  a  single  span  of  several  thou- 
sand feet  must  be  made,  requiring  high  tensile  strength.  In  such  cases 
it  is  usually  better  to  give  the  steel  span  a  greater  resistance  than  an  equal 
length  of  the  main  portion  of  the  line,  so  as  to  avoid  excessive  size  and 
weight  of  the  span.  Even  when  this  is  done  the  resistance  of  the  steel 
span  would  be  very  small  compared  with  that  of  a  long  transmission 
line. 

Phosphor-bronze  finds  little  use  as  conductors  in  transmission  sys- 
tems because  of  its  relatively  high  electrical  resistance.  If  great  tensile 
strength  is  wanted,  iron  or  steel  will  supply  it  at  a  fraction  of  the  cost  of 
phosphor-bronze.  As  a  conductor  simply,  phosphor-bronze  is  worth  only 
0.26  as  much  per  pound  as  soft  copper,  while  its  actual  market  price  is 
greater  than  that  of  copper. 

Silicon-bronze  of  relatively  high  resistance,  requiring  2.17  times  the 
section  and  weight  of  copper  for  equal  conductivity,  is  entitled  to  little 


MATERIALS  FOR  LINE  CONDUCTORS.  205 

or  no  consideration  as  a  transmission  line  material.  This  alloy,  in  order 
to  give  equal  conductivity  at  equal  cost  with  copper,  must  sell  at  only 
0.46  of  the  price  of  copper  per  pound.  But  the  price  of  silicon-bronze 
is  equal  to,  or  greater  than,  the  price  of  copper,  so  that  the  cost  of  the 
high-resistance  silicon-bronze  for  a  line  of  given  resistance  will  be  more 
than  twice  that  of  copper.  For  this  more  than  double  cost  the  bronze 
gives  6.38  times  the  tensile  strength  of  a  soft  copper  line  of  equal  con- 
ductivity. 

Taking  the  market  price  of  steel  at  one-fifth  that  of  copper,  which 
is  amply  high  for  the  steel,  as  a  rule,  a  steel  wire  of  equal  conductivity 
with  the  copper  will  cost  only  1.6  times  as  much  and  will  have  26.7 
times  the  tensile  strength  of  the  copper,  or  four  times  the  tensile  strength 
of  a  wire  of  equal  conductivity  made  from  the  high-resistance  silicon- 
bronze.  From  this  it  is  clear  that  steel  offers  a  cheaper  combination  of 
conductivity  and  strength  than  does  silicon-bronze  of  high  resistance. 
That  grade  of  silicon-bronze  having  the  lowest  resistance  may  cost  0.98 
as  much  per  pound  as  soft  copper,  and  will  have  1.79  times  the  strength 
of  the  copper  for  equal  conductivity.  This  bronze  actually  costs  more 
per  pound  than  copper,  so  that  it  cannot  give  equal  conductivity  at  equal 
cost. 

Very  hard-drawn  copper  has  a  conductivity  equal  to  that  of  the  best 
silicon-bronze,  and  the  tensile  strength  of  this  copper  is  seventeen  per 
cent  greater  than  that  of  the  bronze.  Silicon-bronze  costs  more  per 
pound  than  hard  copper,  but  even  with  equal  prices  the  hard  copper 
gives  equal  conductivity  and  higher  strength  at  the  same  cost.  Further- 
more, the  conductivity  of  silicon-bronze  is  much  more  liable  to  serious 
variations  than  that  of  hard  copper.  Between  hard-drawn  copper  and 
steel  there  is  very  little  apparent  place  for  any  grade  of  bronze  in  electric 
transmission  lines. 

The  hardest  copper  wire  is  very  stiff,  and  is  more  liable  to  crack 
when  twisted  or  bent  than  is  wire  of  only  medium  hardness.  Such  me- 
dium-hard copper  has  a  tensile  strength  of  thirty-four  per  cent  greater 
than  soft  copper  of  equal  conductivity,  and  is  much  used  on  long  trans- 
mission lines.  Aluminum  is  the  only  metal  which,  for  given  conductivity 
in  a  transmission  line,  combines  a  smaller  weight,  a  greater  tensile 
strength,  and  a  higher  permissible  price  than  soft  copper  for  the  same 
total  cost.  For  equal  conductivity  an  aluminum  wire  has  a  greater  ten- 
sile strength  than  one  of  medium-hard  copper,  and  costs  less  than  copper 
of  any  grade  when  the  price  per  pound  of  the  aluminum  is  less  than 
twice  that  of  copper,  which  is  usually  the  case. 


206     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

These  properties  make  aluminum  by  far  the  most  important  com- 
petitor of  copper  in  electric  transmission  and  have  led  to  its  use  in  a  num- 
ber of  cases,  notably  for  the  two  longest  lines  in  the  world,  namely, 
between  Colgate  and  Oakland  and  between  Electra  and  San  Francisco, 
in  California. 

It  has  not  been  found  practicable  to  solder  joints  in  aluminum  wires 
because  of  the  resulting  electrolytic  action  when  aluminum  is  in  contact 
with  other  metals.  Joints  of  aluminum  wires  are  usually  made  by  slip- 
ping the  ends  past  each  other  in  an  oval  aluminum  sleeve  and  then  giving 
the  sleeve  and  wires  two  or  three  complete  twists,  or  by  a  process  of  cold 
welding  with  a  sleeve  joint. 

Long  transmission  lines  are  in  nearly  all  cases  run  with  bare  wire 
supported  by  poles.  Where  very  high  voltages  are  employed  no  insula- 
tion that  can  be  put  on  the  wire  will  make  it  safe  to  handle,  and  the  cost 
of  such  insulation  would  add  materially  to  that  of  the  entire  line.  It  is, 
therefore,  the  practice  to  run  transmission  lines  above  all  other  wires 
and  to  rely  entirely  on  the  supports  for  insulation. 

The  considerations  thus  far  noted  apply  alike  to  wires  carrying  con- 
tinuous and  alternating  currents,  but  there  are  some  other  factors  that 
apply  solely  to  alternating  lines.  Owing  to  the  inductive  effects  of  alter- 
nating currents  in  long,  parallel  wires,  such  wires  should  be  transposed 
between  their  supports  at  frequent  intervals.  The  induction  between 
wires  increases  with  the  frequency  of  the  current  carried,  and  decreases 
with  the  distance  between  the  wires.  According  to  these  conditions, 
wires  should  be  transposed  as  often  as  every  eighth  of  a  mile  in  some 
cases,  and  at  intervals  of  one  mile  or  more  in  others. 

An  alternating  current  when  passing  along  a  line  tends  to  concentrate 
itself  in  the  outer  layers  of  the  wire,  leaving  the  centre  idle.  This  unequal 
current  distribution  increases  with  the  frequency  of  the  current  and  with 
the  area  of  the  cross  section  of  the  wire.  The  practical  effect  of  this  un- 
equal distribution  is  to  make  the  resistance  of  a  wire  a  little  higher  for 
alternating  than  for  continuous  currents.  In  existing  transmission  lines 
the  increase  of  resistance  due  to  this  cause  seldom  amounts  to  one  per 
cent.  • 

When  an  alternating  current  passes  through  a  circuit,  the  action 
termed  self-induction  sets  up  an  electromotive  force  in  the  circuit  that 
opposes  the  flow  of  current,  as  does  the  resistance  of  the  wire,  and  this 
is  called  the  inductance  of  the  circuit.  The  ratio  of  this  inductance  to 
the  resistance  of  a  circuit  increases  with  the  number  of  periods  per  second 
of  the  alternating  current  used  and  with  the  sectional  area  of  the  wires 


MATERIALS  FOR  LINE  CONDUCTORS.  207 

composing  the  circuit.  For  a  circuit  of  No.  6  B.  &  S.  gauge  wire  the 
inductance  amounts  to  only  five  per  cent  of  the  line  resistance,  but  for 
a  circuit  of  No.  ooo  wire  the  inductance  consumes  as  much  of  the  applied 
voltage  as  does  the  resistance,  with  6o-cycle  current. 

Both  the  unequal  distribution  of  alternating  current  over  the  cross- 
section  of  a  conductor  and  the  inductance  of  circuits  make  it  desirable  to 
keep  the  diameters  of  transmission  wires  as  small  as  other  considerations 
permit.  As  soft  copper  has  greater  conductivity  per  unit  of  area  than 
any  of  the  other  available  metals,  it  clearly  has  an  advantage  over  all  of 
them  as  to  inductance  and  increase  of  resistance  with  alternating  cur- 
rent. 

At  very  high  voltages  there  is  an  important  leakage  of  energy  between 
the  conductors  of  a  circuit,  and  this  loss  varies  inversely  with  the  dis- 
tance between  these  conductors.  Thus  it  happens  that  inductance 
makes  it  desirable  to  bring  the  parallel  wires  of  a  circuit  close  together, 
while  the  leakage  of  energy  from  wire  to  wire  makes  it  desirable  to  carry 
them  far  apart. 

To  provide  greater  security  from  interruption,  the  conductors  for 
important  transmissions  are  in  some  cases  carried  on  two  independent 
pole  lines.  Even  where  all  the  conductors  are  on  a  single  line  of  poles 
it  is  frequent  practice  to  divide  them  up  into  a  number  of  comparatively 
small  wires,  and  this  decreases  inductance. 

Data  of  a  number  of  transmission  lines  presented  in  the  appended 
table  illustrate  the  practice  in  some  of  the  more  recent  and  important 
cases  as  to  the  materials,  size,  number,  and  arrangement  of  the 
wires.  The  plants  of  which  particulars  are  given  include  the  greatest 
power  capacities,  the  longest  distances,  and  the  highest  voltages  now 
involved  in  electrical  transmissions.  Each  of  the  lines  named  is  worked 
with  alternating  current  of  two-  or  three-phase.  Each  three-phase  line 
must  have  at  least  three  wires,  and  each  two-phase  line  usually  has  four 
wires. 

On  ten  of  the  lines  the  number  of  wires  is  greater  than  three  or  four, 
thus  reducing  the  necessary  size  of  each  wire  for  a  given  conductivity  of 
the  line.  The  Butte,  Oakland,  and  Hamilton  lines  are  run  on  two  sets 
of  poles  for  greater  security,  and  a  second  pole  line  has  been  added  to 
the  Niagara  and  Buffalo  system  to  carry  additional  wires. 

The  largest  wire  used  in  any  of  these  lines  is  the  aluminum  cable  of 
500,000  circular  mils  between  Niagara  Falls  and  Buffalo.  This  cable 
has  1.66  times  the  area  in  cross  section  of  a  copper  cable  of  equal  con- 
ductivity. 


208     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Aluminum  lines  are  now  employed  for  the  three  longest  electrical 
transmissions  in  North  America.  In  the  longest  single  line,  that  from 
Electra  power-house  to  San  Francisco,  a  distance  of  147  miles,  aluminum 
is  the  conductor  used.  The  142-mile  transmission  between  Colgate 


SIZES  AND  MATERIALS  OF  WIRES  ON  SOME  AMERICAN  TRANSMISSION  LINES. 


Location  of  Transmission. 

a)  bo 

'^'o 
> 

1  Number 
Wires. 

Size  of  Each 
Wire 
B.  &  S.  Gauge. 

Metal  in 
Wire. 

Length  of 
Transmis- 
sion. Miles. 

Cafion  Ferry  to  Butte. 

50,000 

6 

o 

Copper 

6q 

Colgate  to  Oakland  

40,000 

7 

oo 

v^vyrrv'i 

Copper 

wj 

142 

o 
3 

ooo 

A1      ^ 
Aluminum 

xiT* 
142 

Electra  to  San  Francisco  

40,000 

3 

471,034  C.M. 

« 

147 

Santa  Ana  R.  to  Los  Angeles. 

33,000 

6 

i 

Copper 

83 

Apple  River  to  St.  Paul 

25,000 

6 

2 

2C 

Welland  Canal  to  Hamilton  . 

22,500 

3 

I 

*  J 

35 

3 

OO 

37 

Canon  City  to  Cripple  Creek. 

20,000 

3 

*3i 

Madrid  to  Bland  

20,000 

^ 

4 

32 

White  River  to  Dales  

22,000 

7 

6 

O 

27 

Ogden  to  Salt  Lake  City  

16,000 

O 

6 

i 

/ 

36} 

San    Gabriel   Canon  to   Los 

Angeles  

1  6,000 

6 

c 

23 

To  Victor  Col 

12,600 

3 

3 
A 

Niagara  Falls  to  Buffalo  .... 

22,000 

6 

*T 

350,000  C.  M. 

23 

«          «               « 

22,000 

3 

500,000  C.  M. 

Aluminum 

20 

Yadkin  River  to  Salem  .... 

I2,OOO 

7 

i 

Copper 

14.^ 

Farmington  Riv'r  to  Hartford 

IO,000 

o 
3 

336,420  C.M. 

Aluminum 

ifcr'0 
II 

Wilbraham  to  Ludlow  Mills. 

11,500 

6 

135,  247  C.M. 

M 

4-5 

Niagara  Falls  to  Toronto  .  .  . 

6o,OOO 

6 

190,000  C.  M. 

Copper 

75 

and  Oakland  is  carried  out  with  three  aluminum  and  three  copper  line 
wires.  For  the  third  transmission  in  point  of  length,  that  from  Shawini- 
gan  Falls  to  Montreal,  a  distance  of  85  miles,  three  aluminum  conductors 
are  employed. 

The  three  transmissions  just  named  have  unusually  large  capacities 
as  well  as  superlative  lengths,  the  generators  in  the  Electra  plant  being 
rated  at  10,000,  in  the  Colgate  plant  at  11,250,  and  in  the  Shawinigan 
plant  at  7,500  kilowatts.  Weight  and  cost  of  such  lines  are  very  large. 
For  the  three  No.  oooo  aluminum  conductors,  142  miles  each  in  length, 
between  Colgate  and  Oakland,  the  total  weight  must  be  about  440,067 
pounds,  costing  $132,020  at  30  cents  per  pound.  Between  Electra  and 
Mission  San  Jose,  where  the  line  branches,  is  ioo  miles  of  the  14 7-mile 
transmission  from  Electra  to  San  Francisco.  On  the  Electra  and  Mis- 


MATERIALS  FOR  LINE  CONDUCTORS.  209 

sion  San  Jose  section  the  aluminum  conductors  comprise  three  stranded 
cables  of  471,034  circular  mils  each  in  sectional  area  and  with  a  total 
weight  of  about  721,200  pounds.  This  section  alone  of  the  line  in  ques- 
tion would  have  cost  $216,360  at  30  cents  per  pound.  The  85-mile 
aluminum  line  from  Shawinigan  Falls  to  Montreal  is  made  up  of  three- 
stranded  conductors  each  with  a  sectional  area  of  183,708  circular  mils. 
All  three  conductors  have  a  combined  weight  of  about  225,300  pounds, 
and  at  30  cents  per  pound  would  have  cost  $67,590. 

Aluminum  lines  are  not  confined  to  new  transmissions,  but  are  also 
found  in  additions  to  those  where  copper  conductors  were  at  first  used. 
Thus,  the  third  transmission  circuit  between  the  power-house  at  Niagara 
Falls  and  the  terminal  house  in  Buffalo,  a  distance  of  20  miles  by  the 
new  pole  line,  was  formed  of  three  aluminum  cables  each  with  an  area 
of  500,000  circular  mils,  though  the  six  conductors  of  the  two  previous 
circuits  were  each  350,000  circular  mils  copper. 

From  these  examples  it  may  be  seen  that  copper  has  lost  its  former 
place  as  the  only  conductor  to  be  seriously  considered  for  transmission 
circuits.  Aluminum  has  not  only  disputed  this  claim  for  copper,  but  has 
actually  gained  the  most  conspicuous  place  in  long  transmission  lines. 
This  victory  of  aluminum  has  been  won  in  hard  competition.  The 
decisive  factor  has  been  that  of  cost  for  a  circuit  of  given  length  and 
resistance. 

From  the  standpoint  of  cross-sectional  area  aluminum  is  inferior  to 
copper  as  an  electrical  conductor.  Comparing  wires  of  equal  sizes  and 
lengths,  the  aluminum  have  only  sixty  per  cent  of  the  conductivity  of  the 
copper,  so  that  an  aluminum  wire  must  have  1.66  times  the  sectional  area 
of  a  copper  wire  of  the  same  length  in  order  to  offer  an  equal  electrical 
resistance.  As  round  wires  vary  in  sectional  areas  with  the  squares 
of  their  diameters,  an  aluminum  wire  must  have  a  diameter  1.28  times 
that  of  a  copper  wire  of  equal  length  in  order  to  offer  the  same  con- 
ductivity 

The  inferiority  of  aluminum  as  an  electrical  conductor  in  terms  of 
sectional  area  is  more  than  offset  by  its  superiority  over  copper  in  terms 
of  weight.  One  pound  of  aluminum  drawn  into  a  wire  of  any  length 
will  have  a  sectional  area  3.33  times  as  great  as  one  pound  of  copper  in 
a  wire  of  equal  length.  This  follows  from  the  fact  that  the  weight  of 
copper  is  555  pounds  while  that  of  aluminum  is  only  167  pounds  per 
cubic  foot,  so  that  for  equal  weights  the  bulk  of  the  latter  is  3.33  times 
that  of  the  former  metal.  As  the  aluminum  wire  has  equal  length  with 
and  3.33  times  the  sectional  area  of  the  copper  wire  of  the  same  weight, 


210    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  electrical  conductivity  of  the  former  is  3.33  -±-  1.66  =  2  times  that 
of  the  latter.  Hence,  for  equal  resistances,  the  weight  of  an  aluminum 
is  only  one-half  as  great  as  that  of  a  copper  wire  of  the  same  length. 
From  this  fact  it  is  evident  that  when  the  price  per  pound  of  aluminum 
is  anything  less  than  twice  the  price  of  copper,  the  former  is  the  cheaper 
metal  for  a  transmission  line  of  any  required  length  and  electrical  re- 
sistance. 

The  tensile  strength  of  both  soft  copper  and  of  aluminum  wire  is 
about  33,000  pounds  per  square  inch  of  section.  For  wires  of  equal 
length  and  resistance  the  aluminum  is  therefore  sixty-six  per  cent 
stronger  because  its  area  is  sixty-six  per  cent  greater  than  that  of  a  soft 
copper  wire.  Medium  hard-drawn  copper  wire  such  as  is  most  com- 
monly used  for  transmission  lines  has  a  tensile  strength  of  about  45,000 
pounds  per  square  inch,  but  even  compared  with  this  grade  of  copper 
the  aluminum  wire  of  equal  length  and  resistance  has  the  advantage  in 
tensile  strength.  While  the  aluminum  line  is  thus  stronger  than  an 
equivalent  one  of  copper,  the  weight  of  the  former  is  only  one-half  that 
of  the  latter,  so  that  the  distance  between  poles  may  be  increased,  or  the 
sizes  of  poles,  cross-arms,  and  pins  decreased  with  aluminum  wires.  In 
one  respect  the  strain  on  poles  that  carry  aluminum  may  be  greater  than 
that  on  poles  with  equivalent  copper  lines,  namely,  in  that  of  wind  press- 
ure. A  wind  that  blows  in  a  direction  other  than  parallel  with  a 
transmission  line  tends  to  break  the  poles  at  the  ground  and  prostrate 
the  line  in  a  direction  at  right  angles  to  its  course.  The  total  wind 
pressure  in  any  case  is  obviously  proportional  to  the  extent  of  the  surface 
on  which  it  acts,  and  this  surface  is  measured  by  one-half  of  the  external 
area  of  all  the  poles  and  wires  in  a  given  length  of  line.  As  the  aluminum 
wire  must  have  a  diameter  twenty-eight  per  cent  greater  than  that  of 
copper  wire  of  equal  length,  one-half  of  the  total  wire  surface  will  also 
be  twenty-eight  per  cent  greater  for  the  former  metal.  This  carries  with 
it  an  increase  of  twenty-eight  per  cent  in  that  portion  of  the  wind  pressure 
due  to  wire  surface.  In  good  practice  the  number  of  transmission  wires 
per  pole  line  is  often  only  three,  and  seldom  more  than  six,  so  that  the  sur- 
face areas  of  these  wires  may  be  no  greater  than  that  of  the  poles.  It  fol- 
lows that  the  increase  of  twenty-eight  per  cent  in  the  surface  of  wires  may 
correspond  to  a  much  smaller  percentage  of  increase  for  the  entire  area 
exposed  to  wind  pressure.  Such  small  difference  as  exists  between  the 
total  wind  pressures  on  aluminum  and  copper  lines  of  equal  conductivity 
is  of  slight  importance  in  view  of  the  general  practice  by  which  some 
straight  as  well  as  the  curved  portions  of  transmission  lines  are 
14 


MATERIALS  FOR  LINE  CONDUCTORS.  211 

now  secured  by  guys  or  struts  at  right  angles  to  the  direction  of  the 
wires. 

Vibration  of  transmission  lines  and  the  consequent  tendency  of  cross- 
arms,  pins,  insulators,  and  of  the  wires  to  work  loose  is  less  with  alu- 
minum than  with  copper  conductors  as  ordinarily  strung,  because  of 
the  greater  sag  between  poles  given  the  former  and  also  probably  be- 
cause of  their  smaller  weight.  An  illustration  of  this  sort  may  be  seen 
on  the  old  and  new  transmission  lines  between  Niagara  Falls  and  Buf- 
falo. The  two  old  copper  circuits  consist  of  six  cables  of  350,000  circular 
mils  section  each  on  one  line  of  poles,  and  are  strung  with  only  a  moderate 
sag.  In  a  strong  wind  these  copper  conductors  swing  and  vibrate  in 
such  a  way  that  their  poles,  pins,  and  cross-arms  are  thrown  into  a  vibra- 
tion that  tend  to  work  all  attachments  loose.  The  new  circuit  consists 
of  three  500,000  circular  mil  aluminum  conductors  on  a  separate  pole 
line  strung  with  a  large  sag  between  poles,  and  these  conductors  take 
positions  in  planes  at  large  angles  with  the  vertical  in  a  strong  wind, 
but  cause  little  or  no  vibration  of  their  supports.  One  reason  for  the 
greater  sag  of  the  aluminum  over  that  of  the  copper  conductors  in  this 
case  is  the  fact  that  the  poles  carrying  the  former  are  140  feet  apart  while 
the  distance  between  the  poles  for  the  latter  is  only  seventy  feet,  on 
straight  sections  of  the  line. 

The  necessity  for  greater  sag  in  aluminum  than  in  copper  conductors, 
even  where  the  span  lengths  are  equal,  arises  from  the  greater  coefficient 
of  expansion  possessed  by  the  former  metal.  Between  32°  and  212° 
Fahrenheit  aluminum  expands  about  0.0022,  and  copper  0.0016  of  its 
length,  so  that  the  change  in  length  is  40  per  cent  greater  in  the  former 
than  in  the  latter  metal.  The  conductors  in  any  case  must  have  enough 
sag  between  poles  to  provide  for  contraction  in  the  coldest  weather,  and 
it  follows  that  the  necessary  sag  of  aluminum  wires  will  be  greater  than 
that  of  copper  at  ordinary  temperature. 

In  pure  air  aluminum  is  even  more  free  from  oxidation  than  copper, 
but  where  exposed  to  the  fumes  of  chemical  works,  to  chlorine  com- 
pounds, or  to  fatty  acids  the  metal  is  rapidly  attacked.  For  this  reason 
aluminum  conductors  should  have  a  water-proof  covering  where  exposed 
to  any  of  these  chemicals.  The  aluminum  line  between  Niagara  Falls 
and  Buffalo  is  bare  for  most  of  its  length,  but  in  the  vicinity  of  the  large 
chemical  works  at  the  former  place  the  wires  are  covered  with  a  braid 
treated  with  asphaltum.  Aluminum  alloyed  with  sodium,  its  most  com- 
mon impurity,  is  quickly  corroded  in  moist  air,  and  should  be  carefully 
avoided.  All  of  the  properties  of  aluminum  here  mentioned  relate  to  the 


212     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

pure  metal  unless  otherwise  stated,  and  its  alloys  should  not,  as  a  rule,  be 
considered  for  transmission  lines.  As  aluminum  is  electropositive  to 
most  other  metals  the  soldering  of  its  joints  is  quite  sure  to  result  in  elec- 
trolytic corrosion,  unless  the  joints  are  thoroughly  protected  from  mois- 
ture, a  result  that  is  hard  to  attain  with  bare  wires.  The  regular  practice 
is  to  avoid  the  use  of  solder  and  rely  on  mechanical  joints.  A  good  joint 
may  be  made  by  slipping  the  roughened  ends  of  wires  to  be  connected 
through  an  aluminum  tube  of  oval  section,  so  that  one  wire  sticks  out  at 
each  end,  then  twisting  the  tube  and  wires  and  giving  each  of  the  latter 
a  turn  about  the  other.  Aluminum  may  be  welded  electrically  and  also 
by  hammering  at  a  certain  temperature,  but  these  processes  are  not  con- 
venient for  line  construction.  Especial  care  is  necessary  to  avoid  scar- 
ring or  cutting  into  aluminurti  wires,  as  may  be  done  when  they  are  tied 
to  their  insulators.  Aluminum  tie  wires  should  be  used  exclusively.  To 
avoid  the  greater  danger  of  damage  to  solid  wires  and  also  to  obtain 
greater  strength  and  flexibility,  aluminum  conductors  are  most  fre- 
quently used  in  the  form  of  cables.  The  sizes  of  wires  that  go  to  make 
up  these  cables  commonly  range  from  No.  6  to  9  B.  &  S.  gauge  for  widely 
different  cable  sections.  Thus  the  183,708  circular  mil  aluminum  cable 
between  Shawihigan  Falls  and  Montreal  is  made  up  of  seven  No.  6 
wires,  and  the  471,034  circular  mil  cable  between  Electra  and  Mission 
San  Jose  contains  thirty-seven  No.  9  wires.  From  the  Farmington  River 
to  Hartford  each  336,420  circular  mils  cable  has  exceptionally  large 
strands  of  approximately  No.  3  wire.  It  appears  from  the  description 
of  a  43-mile  line  in  California  (vol.  xvii.,  A.  I.  E.  E.,  p.  345)  that  a  solid 
aluminum  wire  of  294  mils  diameter,  or  No.  i  B.  &  S.  gauge,  can  be  used 
without  trouble  from  breaks.  This  wire  was  tested  and  its  properties 
reported  as  follows: 

Diameter,  293.9  mils. 

Pounds  per  mile,  419.4. 

Resistance  per  mil  foot,  17.6  ohms  at  25°  C. 

Resistance  per  mile  at  25°  C.,  1.00773  ohms. 

Conductivity  as  to  copper  of  same  size,  59.9  per  cent. 

Number  of  twists  in  six  inches  for  fracture,  17.9. 

Tensile  strength  per  square  inch,  32,898  pounds. 

This  wire  also  stood  the  test  of  wrapping  six  times  about  its  own 
diameter  and  then  unwrapping  and  wrapping  again.  It  was  found  in 
tests  for  tensile  strength  that  the  wire  in  question  took  a  permanent  set 
at  very  small  loads,  but  that  at  points  between  14,000  and  17,000  pounds 
per  square  inch  the  permanent  set  began  to  increase  very  rapidly.  From 
this  it  appears  that  aluminum  wires  and  cables  should  be  given  enough 


MATERIALS  FOR  LINE  CONDUCTORS. 


213 


sag  between  poles  so  that  in  the  coldest  weather  the  strains  on  them  shall 
not  exceed  about  15,000  pounds  per  square  inch.  This  rather  low  safe 
working  load  is  a  disadvantage  that  aluminum  shares  with  copper. 
From  the  figures  just  given  it  is  evident  that  the  strains  on  aluminum 
conductors  during  their  erection  should  not  exceed  one-half  of  the  ulti- 
mate strength  in  any  case,  lest  their  sectional  areas  be  reduced. 

ALUMINUM  CABLES  IN  TRANSMISSION  SYSTEMS. 


"o 

1 

a 

s.  . 

i| 

Locations. 

J! 

J 

11 

h 

Jl 

c/5 

Si 

Sti 

u 

K  < 

Niagara  Falls  to  Buffalo  

•2 

20 

500,000 

Shawinigan  Falls  to  Montreal  

3 

85 

183,708 

7 

6 

Electra  to  Mission  San  Tosd 

IOO 

471  O^4 

•77 

Colgate  to  Oakland  . 

•} 

144 

211  ,OOO 

7 

Farmington  River  to  Hartford  

3 

II 

7 

3 

Lewiston,  Me  

? 

2.  cr 

144,688 

7 

Q 

Ludlow  Mass 

6 

4e 

TTC  247 

7" 

7" 

This  table  of  transmission  systems  using  aluminum  conductors  is  far 
from  exhaustive.  Aluminum  is  also  being  used  to  distribute  energy  to 
the  sub-stations  of  long  electric  railways,  as  on  the  Aurora  and  Chicago 
which  connects  cities  about  forty  miles  apart.  The  lower  cost  of  alu- 
minum conductors  is  also  leading  to  their  adoption  instead  of  copper  in 
city  distribution  of  light  and  power.  Thus  at  Manchester,  N.  H.,  the 
local  electric  lines  include  about  four  miles  each  of  500,000  and  750,000 
circular  mil  aluminum  cable  with  weather-proof  insulation.  The  larger 
of  these  cables  contains  thirty-seven  strands  of  about  No.  7  wire. 

As  may  be  seen  from  the  foregoing  facts,  the  choice  of  copper  or 
aluminum  for  a  transmission  line  should  turn  mainly  on  the  cost  of  con- 
ductors of  the  required  length  and  resistance  in  each  metal.  So  nearly 
balanced  are  the  mechanical  and  electrical  properties  of  the  two  metals 
that  not  more  than  a  very  small  premium  should  be  paid  for  the  privilege 
of  using  copper.  As  already  pointed  out,  the  costs  of  aluminum  and 
copper  conductors  of  given  length  and  resistance  are  equal  when  the  price 
per  pound  of  aluminum  wire  is  twice  that  of  copper.  During  most  of  the 
time  for  several  years  the  price  of  aluminum  has  been  well  below  double 
the  copper  figures,  and  the  advantage  has  been  with  aluminum  conduc- 
tors. With  the  two  metals  at  the  same  price  per  pound  aluminum  would 


2i4    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

cost  only  one-half  as  much  as  equivalent  copper  conductors.  When  the 
price  of  aluminum  is  fifty  per  cent  greater  per  pound  than  that  of  copper, 
the  use  of  the  former  metal  effects  a  saving  of  twenty-five  per  cent.  For 
the  new  Niagara  and  Buffalo  line,  completed  early  in  1901,  aluminum 
was  selected  because  it  effected  a  saving  of  about  twelve  per  cent  over 
the  cost  of  copper.  All  of  the  aluminum  lines  here  mentioned,  except 
the  short  one  near  Hartford,  were  completed  during  or  since  1 900.  Most 
of  the  facts  here  stated  as  to  the  line  between  Niagara  Falls  and  Buffalo 
are  drawn  from  vol.  xviii.,  A.  I.  E.  E.,  at  pages  520  and  521. 

The  greater  diameter  of  aluminum  over  equivalent  copper  conduc- 
tors has  advantages  in  transmission  with  alternating  current  at  very  high 
voltages.  At  high  voltages,  say  of  40,000  or  more,  the  constant  silent 
loss  of  energy  from  one  conductor  to  another  of  the  same  circuit  through 
the  air  tends  to  become  large  and  even  prohibitive  in  amount.  This  loss 
is  greater,  other  factors  being  constant,  the  smaller  the  diameter  of  the 
conductors  in  the  line.  It  follows  that  this  loss  is  more  serious  the 
smaller  the  power  to  be  transmitted,  because  the  smaller  the  diameter  of 
the  line  wires.  The  silent  passage  of  energy  from  wire  to  wire  increases 
directly  with  the  length  of  line  and  thus  operates  as  a  limit  to  long 
transmissions. 


CHAPTER  XVI. 

VOLTAGE  AND  LOSSES  ON  TRANSMISSION  LINES. 

THE  voltage  on  a  transmission  line  may  be  anything  up  to  at  least 
60,000,  and  the  weight  of  conductors  varies  inversely  with  the  square  of 
the  figures  selected,  the  power,  length  and  loss  being  constant.  What- 
ever the  total  line  pressure,  the  weight  of  conductors  varies  inversely 
with  the  percentage  of  loss  therein. 

The  case  of  maximum- loss  and  minimum  weight  of  conductors  is  that 
in  which  all  of  the  transmitted  energy  is  expended  in  heating  the  line 
wires.  Such  a  case  would  never  occur  in  practice,  because  the  object  of 
power  transmission  is  to  perform  some  useful  work. 

Minimum  loss  is  theoretically  zero,  and  the  corresponding  weight 
of  conductors  is  infinite,  but  these  conditions  obviously  cannot  be 
attained  in  practice.  Between  these  extremes  of  minimum  and  of  in- 
finite weights  of  conductors  comes  every  practical  transmission  with  a 
line  loss  greater  than  zero  and  less  than  100  per  cent. 

To  determine  the  weight  and  allowable  cost  of  conductors,  the  cost 
of  the  energy  that  will  be  annually  lost  in  them  enters  as  one  of  the  fac- 
tors. At  this  point  the  distinction  between  the  percentage  of  power 
lost  at  maximum  load  and  the  percentage  of  total  energy  lost  should 
come  into  view. 

Line  loss  ordinarily  refers  to  the  percentage  of  total  power  consumed 
in  the  conductors  at  maximum  load.  This  percentage  would  correspond 
with  that  of  total  energy  lost  if  the  line  current  and  voltage  were  constant 
during  all  periods  of  operation,  but  this  is  far  from  the  case. 

A  system  of  transmission  may  operate  with  either  constant  volts  or 
constant  amperes  on  the  line  conductors,  but  in  a  practical  case  con- 
stancy of  both  these  factors  is  seldom  or  never  to  be  had.  This  is  because 
the  product  of  the  line  volts  and  amperes  represents  accurately  in  a  con- 
tinuous-current system,  and  approximately  in  an  alternating-current  sys- 
tem, the  amount  of  power  transmitted.  In  an  actual  transmission  sys- 
tem, the  load — that  is,  the  demand  for  power — is  subject  to  more  or  less 
variation  at  different  times  of  the  day,  and  the  line  vots  or  amperes,  or 
both,  must  vary  with  it. 

215 


2i 6     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

If  the  transmission  system  is  devoted  to  the  operation  of  one  or  more 
factories  the  required  power  may  not  vary  more  than  twenty-five  per  cent 
during  the  hours  of  daily  use ;  but  if  a  system  of  general  electrical  supply 
is  to  be  operated,  the  maximum  load  will  usually  be  somewhere  between 
twice  and  four  times  as  great  as  the  average  load  for  each  twenty-four 
hours.  Such  fluctuating  loads  imply  corresponding  changes  in  the  volts 
or  amperes  of  the  transmission  line. 

A  number  of  rather  long  transmissions  is  carried  out  in  Europe 
with  continuous,  constant  current,  and  in  such  systems  the  line  volt- 
age varies  directly  with  the  load.  As  the  loss  of  power  in  an  electrical 
conductor  depends  entirely  on  its  ohms  of  resistance,  which  are  constant 
at  any  given  temperature,  and  on  the  amperes  of  current  passing  through 
it,  the  line  loss  in  a  constant-current  system  does  not  change  during  the 
period  of  operation,  no  matter  how  great  •  may  be  its  changes  of 
load.  For  this  reason  the  percentage  of  power  loss  in  the  line  at  maxi- 
mum load  is  usually  smaller  than  the  percentage  of  energy  loss  for  an 
entire  day. 

If,  for  example,  the  constant-current  transmission  line  is  designed  to 
convert  into  heat  5  per  cent  of  the  maximum  amount  of  energy  that  will 
be  delivered  to  it  per  second — that  is,  to  lose  5  per  cent  of  its  power  at 
maximum  load — then,  when  the  power  which  the  line  receives  drops  to 
one-half  of  its  maximum,  the  percentage  of  loss  will  rise  to  10,  because 
0.05  -f-  0.5  =  o.i.  So  again,  when  the  power  sent  through  the  line  falls 
to  one-quarter  of  the  full  amount,  the  line  loss  will  rise  to  0.05  -^  0.25 
=  0.2,  or  20  per  cent. 

From  these  facts  it  is  clear  that  a  fair  all-day  efficiency  for  a  constant- 
current  transmission  line  can  be  obtained  only  in  conjunction  with  a 
high  efficiency  at  maximum  load,  if  widely  varying  loads  are  to  be  oper- 
ated. It  does  not  necessarily  follow  from  these  facts  as  to  losses  in  con- 
stant-current lines  that  such  losses  should  always  be  small  at  maximum 
loads,  for  if  a  large  loss  may  be  permitted  at  full  load  a  still  greater 
percentage  of  loss  at  partial  loads  may  not  imply  bad  engineering. 

In  a  large  percentage  of  electric  water-power  plants  some  water  goes 
over  the  dam  during  those  hours  of  the  day  when  loads  are  light,  the  stor- 
age capacity  above  the  dam  not  being  sufficient  to  hold  all  of  the  surplus 
water  during  most  seasons  of  the  year.  If,  therefore,  the  line  loss  in  a 
constant-current  transmission,  where  all  of  the  daily  flow  of  water  cannot 
be  used,  is  not  great  enough  to  reduce  the  maximum  load  that  would 
otherwise  be  carried,  then  the  fact  that  the  percentage  of  line  loss  at 
small  loads  is  still  larger  is  not  very  important. 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        217 

Obviously,  it  makes  little  difference  whether  water  goes  over  a  dam 
or  through  wheels  to  make  up  for  a  loss  in  the  line.  In  a  case  where  all 
the  water  can  be  stored  during  small  loads  and  used  during  heavy  loads, 
it  is  clearly  desirable  to  keep  the  loss  in  a  constant-current  line  down  to  a 
rather  low  figure,  say  not  more  than  five  per  cent,  at  maximum  load. 

Much  the  greater  number  of  electrical  transmissions  are  carried  out 
with  nearly  constant  line  voltage,  mostly  alternating,  and  the  line  cur- 
rent in  such  cases  varies  directly  with  the  power  transmitted,  except  as 
to  certain  results  of  inductance  on  alternating  lines.  As  line  resistance 
is  constant,  save  for  slight  variations  due  to  temperature,  the  rate  of 
energy  loss  on  a  constant-pressure  line  varies  with  the  square  of  the 
number  of  amperes  flowing,  and  the  percentage  of  loss  with  any  load 
varies  directly  as  the  number  of  amperes. 

These  relations  between  line  losses  and  the  amperes  carried  follow 
from  the  law  that  the  power,  or  rate  of  work,  is  represented  by  the  prod- 
uct of  the  number  of  volts  by  the  number  of  amperes,  and  the  law  that 
the  power  actually  lost  in  the  line  is  represented  by  the  product  of  the 
number  of  ohms  of  line  resistance  and  the  square  of  the  number  of  am- 
peres flowing  in  it.  In  each  of  these  cases  the  power  delivered  to  the 
line  is,  of  course,  measured  in  watts,  each  of  which  is  1-746  of  a  horse- 
power. 

Applying  these  laws,  it  appears  that  if  the  loss  of  a  certain  constant- 
pressure  transmission  line  is  10  per  cent  of  the  power  delivered  to  it  at 
full  load,  then,  when  the  power,  and  consequently  the  amperes,  on  the 
line  is  reduced  one-half,  the  watts  lost  in  the  line  as  heat  will  be  (J)2  =  J 
of  the  watts  lost  at  full  load,  because  the  number  of  amperes  flowing  has 
been  divided  by  2. 

But  the  amount  of  power  delivered  to  the  line  at  full  load  having  been 
reduced  by  50  per  cent,  while  the  power  lost  on  the  line  dropped  to  one- 
fourth  of  10  per  cent,  or  to  2.5  per  cent  of  the  full  line  load,  it  follows 
that  the  power  lost  on  the  line  at  half-load  is  represented  by  0.025  ^-  0.5 
=  0.05,  or  5  per  cent  of  the  power  then  delivered  to  it. 

This  rise  in  the  efficiency  of  a  constant-pressure  transmission  line  as 
the  power  delivered  to  it  decreases,  together  with  the  fact  that  maximum 
loads  on  such  lines  continue  during  hardly  more  than  one  to  two  hours 
daily,  tends  to  raise  the  allowable  percentage  of  line  loss  at  maximum 
loads. 

This  is  so  because  a  loss  of  fifteen  per  cent  at  maximum  load  may 
easily  drop  to  an  average  loss  of  somewhere  between  five  and  ten  per  cent 
for  the  entire  amount  of  energy  delivered  to  a  line  during  each  day  under 


2i8    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

ordinary  conditions  in  electrical  supply.  In  the  practical  design  of  trans- 
mission lines,  therefore,  the  sizes  of  conductors  are  influenced  by  the 
relation  of  the  largest  load  to  be  operated  to  the  greatest  amount  of 
power  available  for  its  operation,  and  by  questions  of  regulation,  as 
well  as  by  considerations  of  all-day  efficiency. 

If  the  maximum  load  that  must  be  carried  by  a  transmission  system 
during  a  single  hour  per  day  requires  nearly  as  much  power  as  can  be 
delivered  to  the  line  conductors,  either  because  of  lack  of  water  storage  or 
of  water  itself,  even  if  it  is  stored,  it  may  be  desirable  to  design  these 
conductors  for  a  small  loss  at  maximum  load,  rather  than  to  install  a 
steam  plant. 

So  again,  as  the  fluctuation  in  voltage  at  the  delivery  end  of  a  trans- 
mission line  between  no  load  and  full  load  will  amount  to  the  entire  drop 
of  volts  in  the  line  at  full  load,  if  the  pressure  at  the  generating  end  is 
constant,  the  requirements  of  pressure  regulation  on  distribution  circuits 
limit  the  drop  of  pressure  in  the  transmission  conductors.  For  good 
lighting  service  with  incandescent  lamps  at  about  no  volts,  the  usual 
pressure,  it  is  necessary  that  variations  be  held  within  one  volt  either 
way  of  the  pressure  of  the  lamps — that  is,  between  109  and  in  volts. 

Every  long-transmission  system  for  general  electrical  supply  neces- 
sarily includes  one  or  more  sub-stations  where  the  distribution  lines  join 
the  transmission  circuits,  and  where  the  voltage  for  lighting  service  is 
regulated.  As  the  limits  of  voltage  variations  on  lighting  circuits  are  so 
narrow,  it  is  necessary  to  keep  the  changes  of  pressure  on  the  transmis- 
sion lines  themselves  within  moderate  limits,  or  such  as  can  be  com- 
pensated for  at  sub-stations. 

This  is  particularly  true  in  cases  where  energy  transmitted  over  a 
single  circuit  is  distributed  for  both  incandescent  lamps  and  large  electric 
motors,  because  the  starting  and  operation  of  such  motors  causes  large 
fluctuations  of  amperes  and  terminal  voltage  on  the  transmission  cir- 
cuits. To  hold  such  fluctuations  within  limits  which  a  sub-station  can 
readily  compensate  for,  it  is  necessary  that  the  loss  in  the  transmission 
line  be  moderate,  say  often  within  ten  per  cent  of  the  total  voltage  de- 
livered to  it  at  maximum  load. 

Capacity  and  cost  of  equipment  at  generating  stations  go  up  with  the 
percentage  of  line  loss,  and  thus  serve  to  limit  its  economical  amount. 
For  every  horse-power  delivered  to  a  transmission  line  at  a  water-power 
station  there  must  be  somewhat  more  than  one  horse-power  of  capacity 
in  water-wheels,  at  least  one  horse-power  in  generators,  and  frequently 
a  further  capacity  of  one  horse-power  in  step-up  transformers.  Every 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        219 

additional  horse-power  lost  in  the  line  at  maximum  load,  if  the  generating 
plant  is  to  be  worked  up  to  its  full  capacity,  implies  ^n  addition  of  some- 
what more  than  one  horse-power  capacity  in  water-wheels,  one  horse- 
power in  generators,  and  one  horse-power  in  transformers. 

Since  the  cost  of  a  generating  station  is  thus  increased  as  the  maxi- 
mum line  loss  is  raised,  a  point  may  be  reached  where  any  further  saving 
in  the  cost  of  the  line  is  more  than  offset  by  the  corresponding  addition 
to  the  cost  of  the  station  and  of  its  operation.  Just  where  this  point,  as 
indicated  by  a  percentage  of  line  loss,  is  to  be  found  depends  on  the 
factors  of  each  case,  important  among  which  is  the  length  of  the  trans- 
mission line. 

Much  effort  has  been  made  to  fix  some  exact  relation  for  maximum 
economy  between  the  first  cost  of  conductors  for  a  transmission  line  and 
the  amount  of  energy  annually  lost  as  heat  therein.  The  best-known 
statement  applying  to  this  case  is  that  of  Lord  Kelvin,  made  in  a  paper 
read  before  the  British  Association  in  1881.  According  to  the  rule  there 
laid  down,  the  most  economical  size  for  the  conductors  of  a  transmission 
line  is  that  for  which  the  annual  interest  on  first  cost  equals  the  cost  of 
the  energy  annually  wasted  in  them. 

If  transmission  systems  were  designed  for  the  sole  purpose  of  wasting 
energy  in  their  line  conductors  this  rule  would  exactly  apply,  for  it 
simply  shows  how  the  cost  of  energy  wasted,  plus  the  interest  on  the  cost 
of  the  conductor  in  which  it  is  wasted,  may  be  brought  to  a  minimum. 
As  a  matter  of  fact,  transmission  systems  are  primarily  intended  to  de- 
liver energy  rather  than  to  waste  it ;  but  of  the  proportions  of  the  entire 
energy  to  be  delivered  and  wasted  (which  is  exactly  what  we  want  to 
know),  the  rule  of  Kelvin  takes  no  account. 

According  to  his  rule,  the  cheaper  the  cost  of  power  where  it  is  de- 
veloped, the  less  should  be  paid  for  conductors  to  bring  it  to  market. 
The  obvious  truth  is  that  the  less  the  cost  of  power  development  at  a 
particular  point,  the  more  may  be  invested  in  a  line  to  bring  it  to  market. 
If  power  cost  nothing  whatever  at  its  source  it  would  not  be  worth  while 
to  build  any  transmission  line  at  all  if  this  rule  is  correct. 

A  modification  of  Lord  Kelvin's  rule  has  been  proposed  by  which  it 
is  said  that  the  interest  on  the  cost  of  the  conductors  and  the  annual 
value  of  the  energy  lost  in  them  should  be  equal,  value  here  meaning 
what  the  energy  can  be  sold  for.  This  rule  would  make  an  investment 
in  line  conductors  too  large. 

The  entire  cost  of  production  and  transmission  for  the  delivered 
energy  should  not  be  greater  than  the  cost  of  a  like  amount  of  energy  de- 


22o    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

veloped  at  the  point  where  the  delivery  is  made.  In  this  entire  cost  of 
production  and  transmission,  interest  on  the  investment  in  line  conduc- 
tors is  only  one  item. 

It  is  perhaps  impossible  to  state  any  exact  rule  for  the  most  eco- 
nomical relation  between  the  cost  of  conductors  and  the  loss  of  energy 
therein  that  will  apply  to  every  transmission.  A  maximum  limit  to  the 
weight  of  conductors  may,  however,  be  set  for  most  cases.  This  limit 
should  not  allow  the  annual  interest  and  depreciation  charges  on  the 
investment  in  line  conductors,  plus  all  other  costs  of  development  and 
transmission,  to  raise  the  total  cost  of  the  transmitted  energy  above  the 
cost  of  development  for  an  equal  amount  of  energy  at  the  point  where 
the  transmitted  energy  is  delivered. 

While  the  maximum  investment  in  transmission  conductors  may  be 
properly  limited  in  the  way  just  stated,  it  by  no  means  follows  that  this 
maximum  limit  should  be  reached  in  every  case.  In  the  varying  require- 
ments of  actual  cases,  the  problem  may  be  to  deliver  a  fixed  amount  of 
power  at  the  least  possible  cost,  or  to  deliver  the  largest  possible  amount 
of  power  at  a  cost  per  unit  under  that  of  development  at  the  point 
of  use.  Frequently  a  transmission  system  has  a  possible  capacity  in 
excess  of  present  requirements,  and  a  line  that  would  not  be  too  heavy 
for  future  business  might  put  an  unreasonable  burden  of  interest  charges 
on  present  earnings. 

The  foregoing  considerations  apply  to  the  design  of  conductors  for 
a  transmission  line  after  the  voltage  at  which  it  is  to  operate  has  been 
decided  on.  Quite  a  different  set  of  facts  should  influence  the  selection 
of  this  voltage.  A  transmission  that  would  be  entirely  impracticable  with 
any  percentage  of  line  loss  that  might  be  selected,  if  carried  out  at  some 
one  voltage,  might  represent  a  paying  business  at  some  higher  voltage 
and  any  one  of  several  sizes  of  line  conductors.  The  power  that  could  be 
delivered  by  a  line  of  practicable  cost,  operated  at  one  voltage,  might  be 
too  small  for  the  purpose  in  hand,  while  the  available  power  at  a  higher 
voltage  might  be  ample. 

If  any  given  power  is  to  be  transmitted  with  a  given  percentage  of 
maximum  loss  in  line  conductors,  the  weight  of  these  conductors  will 
increase  as  the  square  of  their  length,  and  decrease  as  the  square  of  the 
full  voltage  of  operation  in  every  case. 

Thus,  if  the  length  of  this  transmission  is  doubled,  the  weight  of  the 
conductors  must  be  multiplied  by  four,  the  voltage  remaining  the  same; 
but  if  the  voltage  is  doubled  and  the  line  length  remains  unchanged,  the 
weight  of  conductors  must  be  divided  by  four.  With  the  length  of  line 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        221 

and  the  voltage  of  transmission  either  lowered  or  raised  together,  the 
weight  of  the  conductors  remains  fixed,  for  constant  power  and  loss. 

An  illustration  of  this  last  rule  may  be  drawn  from  the  case  of  lines 
designed  to  transmit  any  given  power  a  distance  of  ten  miles  at  10,000 
volts,  and  a  distance  of  fifty  miles  at  50,000  volts,  in  which  the  total 
weight  of  conductors  would  be  the  same  for  each  line  if  the  percentage 
of  loss  was  constant. 

This  statement  of  the  rule  as  to  proportionate  increase  of  voltage  and 
distance  presents  the  advantages  of  high  voltages  in  their  most  favorable 
light.  Though  a  uniform  ratio  between  the  voltage  of  operation  and 
the  length  of  line  allows  a  constant  weight  of  conductors  to  be  employed 
for  the  transmission  of  a  given  power  with  unchanging  efficiency  of 
conductors,  yet  other  considerations  soon  limit  the  advantage  thus  ob- 
tained. 

Important  among  these  considerations  may  be  mentioned  the  me- 
chanical strength  of  line  conductors,  difficulties  of  line  insulation,  losses 
between  conductors  through  the  air,  limits  of  generator  voltages,  and  the 
cost  of  transformers. 

If  the  ten-mile  transmission  at  10,000  volts,  above  mentioned,  requires 
a  circuit  of  two  No.  i/o  copper  wires,  the  total  weight  of  these  wires  will 
be  represented  by  (5,500  x  10  X  2  X  320)  -=-  1,000  —  35,200  pounds, 
allowing  5,500  feet  of  wire  per  mile  of  single  conductor  to  provide  some- 
thing for  sag  between  poles,  and  320  pounds  being  the  weight  of  bare 
No.  i/o  copper  wire  per  1,000  feet. 

When  the  length  of  line  is  raised  to  50  miles,  the  two-wire  circuit 
will  contain  5,500  X  50  X  2  =  550,000  feet  of  single  conductor, 
and  since  the  voltage  is  raised  to  50,000  at  the  same  time,  the  total 
weight  of  conductors  will  be  35,200  pounds  as  before.  The  weight  of 
single  conductor  per  1,000  feet  is  therefore  only  64  pounds  in  the 
5o-mile  line. 

A  No.  7  copper  wire,  B.  &  S.  gauge,  has  a  weight  of  63  pounds  per 
i  ,000  feet,  and  is  the  nearest  regular  size  to  that  required  for  the  5o-mile 
line  as  just  found.  It  would  be  poor  policy  to  string  a  wire  of  this  size 
for  a  transmission  line,  because  it  is  so  weak  mechanically  that  breaks 
would  probably  be  frequent  in  stormy  weather.  The  element  of  unre- 
liability introduced  by  the  use  of  this  small  wire  on  a  5o-mile  line  would 
cost  far  more  in  the  end  than  a  larger  conductor. 

As  a  rule,  No.  46.  &  S.  gauge  wire  is  the  smallest  that  should  be 
used  on  a  long  transmission  line  in  order  to  give  fair  mechanical  strength, 
and  this  size  has  just  twice  the  weight  of  a  No.  7  wire  of  equal  length. 


222     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Here,  then,  is  one  of  the  practical  limits  to  the  advantages  that  may  be 
gained  by  increasing  the  voltage  with  the  length  of  line. 

As  line  voltage  goes  up,  the  strain  on  line  insulation  increases  rapidly, 
and  the  insulators  for  a  circuit  operated  at  50,000  volts  must  be  larger 
and  of  a  much  more  expensive  character  than  those  for  a  10,000- volt  cir- 
cuit. In  this  way  a  part  of  the  saving  in  conductors  effected  by  the 
use  of  very  high  voltages  on  long  lines  is  offset  by  the  increased  cost  of 
insulation. 

Another  disadvantage  that  attends  the  operation  of  transmission  lines 
at  very  high  voltages  is  the  continuous  loss  of  energy  by  the  silent  pas- 
sage of  current  through  the  air  between  wires  of  a  circuit.  This  loss  in- 
creases at  a  rapid  rate  after  a  pressure  between  40,000  and  50,000  volts 
is  reached  with  ordinary  distances  between  the  wires  of  each  circuit. 
To  keep  losses  of  this  sort  within  moderate  limits,  and  also  to  lessen  the 
probability  of  arcs  on  a  circuit  at  very  high  voltage,  the  distance  of  eigh- 
teen inches  or  two  feet  between  conductors  that  carry  current  at  10,000 
volts  should  be  increased  to  six  feet  or  more  on  circuits  that  operate  at 
50,000  volts. 

Such  an  increase  in  the  distance  between  conductors  makes  the  cost 
of  poles  and  cross-arms  greater,  either  by  requiring  them  to  be  larger 
than  would  otherwise  be  necessary  or  by  limiting  the  number  of  wires 
to  two  or  three  per  pole  and  thus  increasing  the  number  of  pole  lines. 
These  added  expenses  form  another  part  of  the  penalty  that  must  be  paid 
for  the  use  of  very  high  voltages  and  the  attendant  saving  in  the  cost  of 
conductors. 

Apparatus  grows  more  expensive  as  the  voltage  at  which  it  is  to  oper- 
ate increases,  because  of  the  cost  of  insulating  materials  and  the  room 
which  they  take  up,  thereby  adding  to  the  size  and  weight  of  the  iron 
parts. 

Generators  for  alternating  current  can  be  had  that  develop  as  much 
as  13,500  volts,  but  such  generators  cost  more  than  others  of  equal  power 
that  operate  at  between  2,000  and  2,500  volts.  These  latter  voltages  are 
as  high  as  it  is  usually  thought  desirable  to  operate  distribution  circuits 
and  service  transformers  in  cities  and  towns,  so  that  if  more  than  2,500 
volts  are  employed  on  the  transmission  line,  step-down  transformers  are 
required  at  a  sub-station.  For  a  transmission  of  more  than  ten  miles 
the  saving  in  line  conductors  by  operation  at  10,000  to  12,000  volts  will 
usually  more  than  offset  the  additional  cost  of  generators  designed 
fcr  th's  pressure  and  of  step-down  transformers.  If  the  voltage 
cf  transmission  is  to  exceed  that  of  distribution,  it  will  generally  be 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        22$ 

found  desirable  to  carry  the  former  voltage  up  to  10,000  or  12,000, 
at  least. 

As  the  cost  of  generators  designed  for  the  voltage  last  named  is  less 
than  that  of  lower  voltage  generators  plus  transformers,  step-up  trans- 
formers should  usually  be  omitted  in  systems  where  these  pressures  are 
not  exceeded.  For  alternating  pressures  above  13,000  to  15,000  volts, 
step-up  transformers  must  generally  be  employed.  In  order  that  the 
saving  in  the  weight  of  line  conductors  may  more  than  offset  the  addi- 
tional cost  of  transformers  when  the  voltage  of  transmission  is  carried 
above  15,000,  this  voltage  should  be  pushed  on  up  to  as  much  as  25,000 
in  most  cases. 

Power  transmission  with  continuous  current  has  the  advantage  that 
the  cost  of  generators  remains  nearly  the  same  whatever  the  line  voltage, 
and  that  no  transformers  are  required.  Such  transmissions  are  common 
in  Europe,  but  have  hardly  a  footing  as  yet  in  the  United  States.  The 
reason  for  the  uniform  cost  of  continuous-current  generators  is  found  in 
the  fact  that  they  are  connected  in  series  to  give  the  desired  line  voltage, 
and  the  voltage  of  each  machine  is  kept  under  3,000  or  4,000.  As  a  par- 
tial offset  to  the  low  cost  of  the  continuous-current  generators  and  to  the 
absence  of  transformers,  there  is  the  necessity  for  motor-generators  in  a 
sub-station  when  current  for  lighting  as  well  as  power  is  to  be  distributed. 

In  spite  of  the  various  additions  to  the  cost  of  transmission  systems 
made  necessary  by  the  adoption  of  very  high  voltages,  these  additions  are 
much  more  than  offset  by  the  saving  in  the  cost  of  conductors  on  lines 
30,  50,  or  100  miles  in  length.  In  fact,  it  is  only  by  means  of  voltages 
ranging  from  25,000  to  50,000  that  the  greatest  of  these  distances,  and 
others  up  to  more  than  140  miles,  have  been  successfully  covered  by 
transmission  lines.  Above  60,000  volts  there  has  been  but  slight  prac- 
tical experience  in  the  operation  of  transmission  lines. 

Calculations  to  determine  the  sizes  of  conductors  for  electric  trans- 
mission lines  are  all  based  on  the  fundamental  law  discovered  by  Ohm, 
which  is  that  the  electric  current  flowing  in  a  circuit  at  any  instant  equals 
the  electric  pressure  that  causes  the  current  divided  by  the  electric  re- 
sistance of  the  circuit  itself,  or  current  =  pressure  -=-  resistance. 

Substituting  in  this  formula  the  units  that  have  been  selected  because 
of  their  convenient  sizes  for  practical  use,  it  becomes,  amperes  =  volts 
-i-  ohms,  in  which  the  ohm  is  simply  the  electrical  resistance,  taken  as 
unity,  of  a  certain  standard  copper  bar  with  fixed  dimensions. 

The  ampere  is  the  unit  flow  of  current  that  is  maintained  with  the 
unit  pressure  of  one  volt  between  the  terminals  of  a  one-ohm  conductor. 


224    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

When  this  formula  is  applied  to  the  computation  of  transmission  lines 
the  volts  represent  the  electrical  pressure  that  is  required  to  force  the 
desired  amperes  of  current  through  the  ohms  of  resistance  in  any  par- 
ticular line,  and  these  volts  have  no  necessary  or  fixed  relation  to  the 
total  voltage  at  which  the  line  may  operate.  Thus,  if  the  total  voltage 
of  a  transmission  system  is  10,000,  it  may  be  desirable  to  use  500,  1,000, 
or  even  2,000  volts  to  force  current  through  the  line,  so  that  one  of  these 
numbers  will  represent  the  actual  drop  or  loss  of  volts  in  the  line  con- 
ductors when  the  number  of  amperes  that  represent  full  load  is  flowing. 
As  it  is  a  law  of  every  electric  circuit  that  the  rate  of  transformation 
of  electric  energy  to  heat  or  work  in  each  of  its  several  parts  is  di- 
rectly proportional  to  the  drop  of  voltage  therein,  it  follows  that  a  drop 
of  500  or  1,000  or  2,000  volts  in  the  conductors  of  a  10,000- volt  trans- 
mission line  at  full  load  would  correspond  to  a  power  loss  of  five  to  ten 
or  twenty  per  cent  respectively.  Any  other  part  of  10,000  volts  might 
be  selected  in  this  case  as  the  pressure  to  be  lost  in  the  line.  Evidently 
no  formula  can  give  the  number  of  volts  that  should  be  lost  in  line  con- 
ductors at  full  load  for  a  given  power  transmission,  but  this  number 
must  be  decided  on  by  consideration  of  the  items  of  line  efficiency,  regula- 
tion, and  the  ratio  of  the  available  power  to  the  required  load. 

Having  decided  on  the  maximum  loss  of  volts  in  the  line  conductors, 
and  knowing  the  full  voltage  of  operation,  the  power  and  consequently 
the  number  of  amperes  delivered  to  the  line  at  maximum  load,  the  resist- 
ance of  the  conductors  may  then  be  calculated  by  the  formula,  amperes 
=  volts  -f-  ohms.  Thus,  if  the  proposition  is  to  deliver  2,000,000  watts 
or  2,000  kilowatts  to  a  two-wire  transmission  line  with  a  voltage  of 
20,000,  the  amperes  in  each  wire  must  be  represented  by  2,000,000  -4- 
20,000  =  100.  With  a  drop  of  ten  per  cent  or  2,000  volts  in  the  two 
line  conductors,  their  combined  resistance  must  be  found  from  100  = 
2,000  -^  ohms,  and  the  ohms  are  therefore  twenty.  If  the  combined 
length  of  the  two  conductors  is  200,000  feet,  corresponding  to  a  trans- 
mission line  of  a  little  under  twenty  miles,  the  resistance  of  these  conduc- 
tors must  be  20  -f-  200  =  o.i  ohm  per  1,000  feet.  From  a  wire  table  it 
may  be  seen  that  a  No.  i/o  wire  of  copper,  B.  &  S.  gauge,  with  a  diameter 
of  0.3249  inch,  has  a  resistance  of  o.iooi  ohm  per  1,000  feet  at  the  tem- 
perature of  90°  Fahrenheit,  a  little  less  at  lower  temperatures,  and  is  thus 
the  required  size.  Obviously,  the  resistance  of  twenty  ohms  is  entirely 
independent  of  the  length  of  the  line,  all  the  other  factors  being  constant, 
and  wires  of  various  sizes  will  be  required  for  other  distances  of  trans- 
mission. 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        225 

It  is  often  convenient  to  find  the  area  of  cross  section  for  the  desired 
transmission  conductor  instead  of  finding  its  resistance.  This  can  be 
done  by  substituting  in  the  formula,  amperes  =  volts  -=-  ohms,  the  ex- 
pi  ession  for  the  number  of  ohms  in  any  conductor,  and  then  solving  as 
before. 

Electrical  resistance  in  every  conductor  varies  directly  with  its  length, 
Inversely  with  its  area  of  cross  section,  and  also  has  a  constant  factor  that 
depends  on  the  material  of  which  the  conductor  is  composed.  This  con- 
slant  factor  is  always  the  same  for  any  given  material,  as  pure  iron, 
<  upper,  or  aluminum,  and  is  usually  taken  as  the  resistance  in  ohms  of  a 
round  wire  one  foot  long  and  o.ooi  inch  in  diameter,  of  the  material  to 
be  used  for  conductors.  Such  a  wire  is  said  to  have  an  area  in  cross 
section  of  one  circular  mil,  because  the  square  of  its  diameter  taken  as 
unity  is  still  unity,  that  is,  i  x  i  —  i  •  In  like  manner,  for  the  conven- 
ient designation  of  wires  by  their  areas  of  cross-section,  each  round  wire 
of  any  size  is  said  to  have  an  area  in  circular  mils  equal  to  the  square  of 
its  diameter  measured  in  units  of  o.ooi  inch  each.  Thus,  a  round  wire 
of  o.i  inch  diameter  has  an  area  of  100  x  100  =  10,000  circular  mils, 
and  a  round  wire  one  inch  in  diameter  has  an  area  of  1,000  x  1,000  = 
1,000,000  circular  mils.  The  circular  mils  of  a  wire  do  not  express  its 
area  of  cross  section  in  terms  of  square  inches,  but  this  is  not  necessary 
since  the  resistance  of  a  wire  of  one  circular  mil  is  taken  as  unity.  Ob- 
viously, the  areas  of  all  round  wires  are  to  each  other  as  are  their  circular 
mils. 

From  the  foregoing  it  may  be  seen  that  the  resistance  of  any  round 
conductor  is  represented  by  the  formula,  ohms  =  /  x  £  -i-  circular  mils, 
in  which  /  represents  the  length  of  the  conductor  in  feet,  s  is  the  resis- 
tance in  ohms  of  a  wire  of  the  same  material  as  the  conductor  but  with 
an  area  of  one  circular  mil  and  a  length  of  one  foot,  and  the  circular 
mils  are  those  of  the  required  conductor.  Substituting  the  quantity,  /  x 
5  -j-  circular  mils,  for  ohms  in  the  formula,  amperes  =  volts  -f-  ohms, 
the  equation,  amperes  =  volts  -j-  (I  Xs  -5-  circular  mils),  is  obtained,  and 
this  reduces  to  circular  mils  =  amperes  x  I  X  5  -f-  volts.  For  any  pro- 
posed transmission  all  of  the  quantities  in  this  formula  are  known,  except 
the  desired  circular  mils  of  the  line  conductors.  The  constant  quantity 
5  is  about  10.8  for  copper,  but  is  conveniently  used  as  eleven  in  calcula- 
tion, and  this  allows  a  trifle  for  the  effects  of  impurities  that  may  exist  in 
the  line  wire. 

The  case  above  mentioned,  where  2,000  kilowatts  were  to  be  delivered 
to  a  transmission  line  at  20,000  volts,  and  a  loss  of  2,000  volts  at  full  load 
15 


226    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

was  allowed  in  the  line  conductors,  may  now  be  solved  by  the  formula 
for  circular  mils.  Taking  the  resistance  of  a  round  copper  wire  o.ooi 
inch  in  diameter  and  one  foot  long  as  eleven  ohms,  and  substituting  the 
100  amperes,  2,000  volts,  and  200,000  feet  of  the  present  case  in  the 
formula,  gives  circular  mils  =  (100  x  200,000  x  IJ)  -f-  2,000  =  no,- 
ooo.  The  square  root  of  this  110,000  will  give  the  diameter  of  a  copper 
wire  that  will  exactly  meet  the  conditions  of  the  case,  or  the  more  prac- 
tical course  of  consulting  a  table  of  standard  sizes  of  wire  will  show  that 
a  No.  i-o  B.  &  S.  gauge,  with  a  diameter  of  0.3249  inch,  has  a  cross 
section  of  105,500  circular  mils,  or  about  five  per  cent  less  than  the  cal- 
culated number,  and  is  the  size  nearest  to  that  wanted.  As  this  No.  i-o 
wire  will  give  a  line  loss  at  full  load  of  about  10.5  per  cent,  or  only  one- 
half  of  one  per  cent  more  than  the  loss  at  first  selected,  it  should  be 
adopted  for  the  line  in  this  case. 

The  formula  just  made  use  of  is  perfectly  general  in  its  application, 
and  may  be  applied  to  the  calculation  of  lines  of  aluminum  or  iron  or  any 
other  metal  just  as  well  as  to  lines  of  copper.  In  order  to  use  the  formula 
for  any  desired  metal,  it  is  necessary  that  the  resistance  in  ohms  of  a 
round  wire  of  that  metal  one  foot  long  and  o.ooi  inch  in  diameter  be 
known  and  substituted  for  5  in  the  formula.  This  resistance  of  a  wire 
one  foot  long  and  o.ooi  inch  in  diameter  is  called  the  specific  resistance 
of  the  substance  of  which  the  wire  is  composed.  For  pure  aluminum 
this  specific  resistance  is  about  17.7,  for  soft  iron  about  sixty,  and  for 
hard  steel  about  eighty  ohms.  The  use  of  these  values  for  s  in  the  form- 
ula will  therefore  give  the  areas  in  circular  mils  for  wires  of  these  three 
substances,  respectively,  for  any  proposed  transmission  line.  In  the 
same  way  the  specific  resistance  of  any  other  metal  or  alloy,  when  known, 
may  be  applied  in  the  formula. 

The  foregoing  calculations  apply  accurately  to  all  two-wire  circuits 
that  carry  continuous  currents,  whether  these  circuits  operate  with  con- 
stant current,  constant  pressure,  or  with  pressure  and  current  both  vari- 
able. Where  circuits  are  to  carry  alternating  currents,  certain  other 
factors  may  require  consideration.  Almost  all  transmissions  with  alter- 
nating currents  are  carried  out  with  three-phase  three-wire,  or  two-phase 
four-wire,  or  single-phase  two-wire  circuits.  Of  the  entire  number  of 
such  transmissions,  those  with  the  three-phase  three-wire  circuits  are  in 
the  majority,  next  in  point  of  number  come  the  two-phase  transmissions, 
and  lastly  a  few  transmissions  are  carried  out  with  single-phase  currents. 
The  voltage  of  a  continuous-current  circuit,  by  which  the  power  of  the 
transmission  is  computed  and  on  which  the  percentage  of  line  loss  is 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        227 

based,  is  the  maximum  voltage  operating  there ;  but  this  is  not  true  for 
circuits  carrying  alternating  currents.  Both  the  volts  and  amperes  in  an 
alternating  circuit  are  constantly  varying  between  maximum  values  in 
opposite  directions  along  the  wires.  It  follows  from  this  fact  that  both 
the  volts  and  amperes  drop  to  zero  as  often  as  they  rise  to  a  maximum. 
It  is  fully  demonstrated  in  books  on  the  theory  of  alternating  currents, 
that  with  certain  ideal  constructions  in  alternating  generators,  and  cer- 
tain conditions  in  the  circuits  to  which  they  are  connected,  the  equivalent 
or,  as  they  are  called,  the  virtual  values  of  the  constantly  changing  volts 
and  amperes  in  these  circuits  are  0.707  of  their  respective  maximum 
values.  Or,  to  state  the  reverse  of  this  proposition,  the  maximum  volts 
and  amperes  respectively  in  these  circuits  rise  to  1.414  times  their  equiv- 
alent or  virtual  values.  These  relations  between  maximum  and  virtual 
volts  and  amperes  are  subject  to  some  variations  with  actual  circuits  and 
generators,  but  the  virtual  values  of  these  factors,  as  measured  by  suitable 
volt-  and  amperemeters,  are  important  in  the  design  of  transmission  cir- 
cuits, rather  than  their  maximum  values.  When  the  volts  or  amperes  of 
an  alternating  circuit  are  mentioned,  the  virtual  values  of  these  factors 
are  usually  meant  unless  some  other  value  is  specified.  Thus,  as  com- 
monly stated,  the  voltage  of  a  single-phase  circuit  is  the  number  of  virtual 
volts  between  its  two  conductors,  the  voltage  of  a  two-phase  circuit  is  the 
number  of  virtual  volts  between  each  pair  of  its  four  conductors,  and  the 
voltage  of  a  three-phase  circuit  is  the  number  of  virtual  volts  between 
either  two  of  its  three  conductors. 

Several  factors  not  present  with  continuous  currents  tend  to  effect  the 
losses  in  conductors  where  alternating  currents  are  flowing,  and  the  im- 
portance of  such  effects  will  be  noted  later.  In  spite  of  such  effects,  the 
formula  above  discussed  should  be  applied  to  the  calculation  of  trans- 
mission lines  for  alternating  currents,  and  then  the  proper  corrections  of 
the  results,  if  any  are  necessary,  should  be  made.  With  this  proviso  as 
to  corrections,  the  virtual  volts  and  amperes  of  circuits  carrying  alternat- 
ing currents  may  be  used  in  the  formula  in  the  same  way  as  the  actual 
volts  and  amperes  of  continuous  current  circuits.  Thus,  reverting  to  the 
above  example,  where  2,000  kilowatts  was  to  be  delivered  at  20,000  volts 
to  a  transmission  line  in  which  the  loss  was  to  be  2,000  volts,  the  kilowatts 
should  be  taken  as  the  actual  rate  of  work  represented  by  the  alternating 
current,  and  the  volts  named  as  the  virtual  volts  on  the  line.  The  virtual 
amperes  will  now  be  100,  as  were  the  actual  amperes  of  continuous  cur- 
rent, and  the  size  of  line  conductor  for  a  single-phase  alternating  trans- 
mission will  therefore  be  i-o,  the  same  as  for  the  continuous-current  line. 


228     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

If  the  transmission  is  to  be  carried  out  on  the  two-phase  four- wire  system, 
the  virtual  amperes  in  each  of  these  wires  will  be  fifty  instead  of  100,  as 
the  power  will  be  divided  equally  between  the  two  pairs  of  conductors, 
and  each  of  these  four  wires  should  have  a  cross-section  in  circular  mils 
just  one-half  as  great  as  that  of  the  No.  i-o  wire.  The  required  wire  will 
thus  be  a  No.  3  B.  &  S.  gauge,  of  52,630  circular  mils,  this  being  the 
nearest  standard  size.  In  weight  the  two  No.  i-o  wires  and  the  four 
No.  3  wires  are  almost  equal,  and  they  should  be  exactly  equal  to  give 
the  same  loss  in  the  single-phase  and  the  two-phase  lines.  For  a  three- 
phase  circuit  to  make  the  transmission  above  considered,  each  of  the 
three  conductors  should  have  an  area  just  one-half  as  great  as  that  of 
each  of  the  two  conductors  for  a  single  phase  circuit,  the  loss  remaining 
as  before,  and  the  nearest  standard  size  of  wire  is  again  No.  3,  as  it  was  for 
the  two-phase  line.  This  is  not  a  self-evident  proposition,  but  the  proof 
can  be  found  in  books  devoted  to  the  theory  of  the  subject.  From  the  fore- 
going it  is  evident  that  while  the  single-phase  and  two-phase  lines  require 
equal  weights  of  conductors,  all  other  factors  being  the  same,  the  weight 
of  conductors  in  the  three-phase  line  is  only  seventy-five  per  cent  of  that 
in  either  of  the  other  two.  Neglecting  the  special  factors  that  tend  to 
raise  the  size  and  weight  of  alternating-current  circuits,  the  single-phase 
and  two-phase  lines  require  the  same  weight  of  conductors  as  does  a 
continuous-current  transmission  of  equal  power,  voltage,  and  line  loss. 
It  should  be  noted  that  in  each  of  these  cases  the  factor  /  in  the  formula 
for  circular  mils  denotes  the  entire  length  of  the  pair  of  conductors  for 
a  continuous-current  line,  or  double  the  distance  of  the  transmission 
with  either  of  the  alternating-current  lines. 

Having  found  the  circular  mils  of  any  desired  conductor,  its  weight 
per  1,000  feet  can  be  found  readily  in  a  wire  table.  In  some  cases  it  is 
desirable  to  calculate  the  weight  of  the  conductors  for  a  transmission  line 
without  finding  the  circular  mils  of  each,  and  this  can  be  done  by  a  modi- 
fication of  the  above  formula.  A  copper  wire  of  i  ,000,000  circular  mils 
weighs  nearly  3.03  pounds  per  foot  of  its  length,  and  the  weight  of  any 
copper  wire  may  therefore  be  found  from  the  formula,  pounds  =  (circular 
mils  x  3-03  X  0  -i-  i, 000,000,  in  which  pounds  indicates  the  total  weight 
of  the  conductor,  /,  its  total  length,  and  the  circular  mils  are  those  of  its 
cross-section.  This  formula  reduces  to  the  form,  circular  mils  —  (i  ,000,- 
ooo  x  pounds)  -=-  (3.03  x  0,  and  if  this  value  for  circular  mils  is  sub- 
stituted in  the  formula  above  given  for  the  cross-section  of  any  wire,  the 
result  is  (1,000,000  x  pounds)  -f-  (3.03  x  0  =  (I  X  amperes  x  n)  -j- 
volts.  Transposition  of  the  factors  in  this  last  equation  brings  it  to  the 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.        229 

form,  pounds  =  (3.03  x  I*  X  amperes  x  ")  -r-  (1,000,000  x  volts), 
which  is  the  general  formula  for  the  total  weight  of  copper  conductors 
when  /,  the  length  of  one  pair,  the  total  amperes  flowing,  and  the  volts 
lost  in  the  conductors  are  known  for  either  a  continuous-current,  a  single- 
phase,  or  a  two-phase  four-wire  line. 

If  the  value  of  /,  200,000,  of  amperes,  100,  and  of  volts,  2,000,  for  the 
transmission  above  considered  are  substituted  in  the  formula  for  total 
weight,  just  found, the  result  is  pounds  =  (3.03  (200,000)"  x  100  x  n) 
-i-  (1,000,000  x  2,000),  which  reduced  to  pounds  —.  66,660,  the  weight 
of  copper  wire  necessary  for  the  transmission  with  either  continuous, 
single-phase  or  two-phase  current.  Witli  three-phase  current  the  weight 
of  copper  in  the  line  for  this  transmission  will  be  75  per  cent  of  the  66,660 
pounds  just  found.  One  or  more  two-wire  circuits  may  be  employed 
for  the  continuous  current  or  for  the  single-phase  transmission,  and  if 
one  such  circuit  is  used  the  weight  for  each  of  the  two  wires  is  obviously 
33,660  pounds.  For  a  two-phase  transmission  two  or  more  circuits  of 
two  wires  each  will  be  used,  and  in  the  case  of  two  circuits,  if  all  four  of 
the  wires  are  of  equal  cross  section,  as  would  usually  be  the  case,  the 
total  weight  of  each  is  16,830  pounds.  If  the  transmission  is  made  with 
one  three-phase  circuit,  the  weight  of  each  of  the  three  wires  is  16,830 
pounds,  and  their  combined  weight,  50,490  pounds  of  copper.  In  each 
of  these  transmission  lines  the  length  of  a  single  conductor  in  one  direc- 
tion is  100,000  feet,  or  one-half  of  the  length  of  the  wires  in  a  single  two- 
wire  circuit.  For  the  two-wire  line  the  calculated  weight  of  each  con- 
ductor amounts  to  66,660  -j-  200  =  333.3  pounds  per  1,000  feet.  For  a 
two-phase  four-wire  line  and  also  for  a  three-phase  three-wire  line,  the 
weight  of  each  conductor  is  16,830  -j-  100  =  168.3  pounds  per  1,000  feet. 
On  inspection  of  a  table  of  weights  for  bare  copper  wires  it  may  be  seen 
that  a  No.  i-o  B.  &  S.  gauge  wire  has  a  weight  of  320  pounds  per  1,000 
feet,  and  being  much  the  nearest  size  to  the  calculated  weight  of  333 
pounds  should  be  selected  for  the  two-wire  circuit.  It  may  also  be  seen 
that  a  No.  3  wire,  with  a  weight  of  159  pounds  per  1,000  feet,  is  the  size 
that  comes  nearest  to  the  calculated  weight  of  168  pounds,  and  should 
therefore  be  employed  in  the  three-wire  and  the  four-wire  circuits,  for 
two-  and  three-phase  transmissions.  Either  a  continuous-current,  single- 
phase,  two-phase,  or  three-phase  transmission  line  may  of  course  be  split 
up  into  as  many  circuits  as  desired,  and  these  circuits  may  or  may  not  be 
designed  to  carry  equal  portions  of  the  entire  power.  In  either  case  the 
combined  weights  of  the  several  circuits  should  equal  those  above  found, 
the  conditions  as  to  power,  loss,  and  length  of  line  remaining  constant. 


230    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

It  will  be  noted  that  the  formulae  for  the  calculation  of  the  circular  mils 
and  for  the  weight  of  the  conductors  in  the  transmission  line  lead  to  the 
selection  of  the  same  sizes  of  wires,  as  they  obviously  should  do. 

Several  laws  governing  the  relations  of  volts  lost,  length  and  weight 
of  line  conductors,  may  be  readily  deduced  from  the  above  formulae. 
Evidently  the  circular  mils  and  weight  of  line  conductors  vary  inversely 
with  the  number  of  volts  lost  in  them  when  carrying  a  given  current,  so 
that  doubling  this  number  of  volts  reduces  the  circular  mils  and  weight 
of  conductors  by  one-half.  If  the  length  of  the  line  changes,  the  circular 
mils  of  the  required  conductors  change  directly  with  it,  but  the  weight  of 
these  conductors  varies  as  the  square  of  their  length.  Thus,  if  the 
length  of  the  line  conductors  is  doubled,  the  cross-section  in  circular 
mils  of  each  conductor  is  also  doubled,  and  each  conductor  is  therefore 
four  times  as  heavy  as  before  for  the  same  current  and  loss  in  volts. 
Should  the  length  of  the  conductors  and  also  the  number  of  volts  lost  in 
them  be  varied  at  the  same  rate,  the  circular  mils  of  each  conductor  re- 
main constant,  and  its  weight  increases  directly  with  the  distance  of 
transmission.  Thus,  with  the  same  size  of  line  wire,  both  the  number 
of  volts  lost  and  the  total  weight  are  twice  as  great  for  a  100-  as  for  a  fifty- 
mile  transmission.  If  the  total  weight  of  conductors  is  to  be  held  con- 
stant, then  the  number  of  volts  lost  therein  must  vary  as  the  square  of 
their  length,  and  their  circular  mils  must  vary  inversely  as  the  length. 
So  that  if  the  length  of  a  transmission  line  is  doubled,  the  circular  mils 
for  conductors  of  constant  weight  are  divided  by  two,  and  the  volts  lost 
are  four  times  as  great  as  before.  Each  of  these  rules  assumes  that  the 
watts  and  percentage  of  loss  in  the  line  are  constant. 

The  above  principles  and  formulae  apply  to  the  design  of  transmission 
lines  for  either  continuous  or  alternating  currents,  but  where  the  alterna- 
ting current  is  employed  certain  additional  factors  should  be  considered. 
One  of  these  factors  is  inductance,  by  which  is  meant  the  counter-electro- 
motive force  that  is  always  present  and  opposed  to  the  regular  voltage  in 
an  alternating  current  circuit.  One  effect  of  inductance  is  to  cut  down 
the  voltage  at  that  end  of  the  line  where  the  power  is  delivered  to  a  sub- 
station, just  as  is  also  done  by  the  ohmic  resistance  of  the  line  conductors. 
Between  the  loss  of  voltage  due  to  line  resistance  and  the  loss  due  to  in- 
ductance there  is  the  very  important  difference  that  the  former  represents 
an  actual  conversion  of  electrical  energy  into  heat,  while  the  latter  is 
simply  the  loss  of  pressure  without  any  material  decrease  in  the  amount 
of  energy.  While  the  loss  of  energy  in  a  transmission  line  depends 
directly  on  its  resistance,  the  loss  of  pressure  due  to  inductance  depends 


VOLTAGE  AND  LOSSES  ON  TRANSMISSION.       231 

on  the  diameter  of  conductors  without  regard  to  their  resistance,  on  the 
length  of  the  circuit,  the  distance  between  the  conductors,  and  on  the 
frequency  or  number  of  cycles  per  second  through  which  the  current 
passes.  As  a  result  of  these  facts,  it  is  not  desirable  or  even  practicable 
to  use  inductance  as  a  factor  in  the  calculation  of  the  resistance  or  weight 
of  a  transmission  line.  On  transmission  lines,  as  ordinarily  constructed, 
the  loss  of  voltage  due  to  inductance  generally  ranges  between  25  and 
100  per  cent  of  the  number  of  volts  lost  at  full  load  because  of  the  resist- 
ance of  the  conductors.  This  loss  through  inductance  may  be  lowered 
by  reducing  the  diameter  of  individual  wires,  though  the  resistance  of  all 
the  circuits  concerned  in  the  transmission  remains  the  same,  by  bringing 
the  wires  nearer  together  and  by  adopting  smaller  frequencies.  In  prac- 
tice the  volts  lost  through  inductance  are  compensated  for  by  operating 
generators  or  transformers  in  the  power-plant  at  a  voltage  that  insures 
the  delivery  of  energy  in  the  receiving-station  at  the  required  pressure. 
Thus,  in  a  certain  case,  it  may  be  desirable  to  transmit  energy  with  a 
maximum  loss  of  ten  per  cent  in  the  line  at  full  load,  due  to  the  resistance 
of  the  conductors,  when  the  effective  voltage  at  the  generator  end  of  the 
line  is  10,000,  so  that  the  pressure  at  the  receiving-station  will  be  9,000 
volts.  If  it  appears  that  the  loss  of  pressure  due  to  inductance  on  this 
line  will  be  i  ,000  volts,  then  the  generators  should  be  operated  at  1 1 ,000 
volts,  which  will  provide  for  the  loss  of  i  ,000  volts  by  inductance,  leave 
an  effective  voltage  of  10,000  on  the  line,  and  allow  the  delivery  of  energy 
at  the  sub-station  with  a  pressure  of  9,000  volts,  when  there  is  a  ten-per- 
cent loss  of  power  due  to  the  line  resistance. 

Inductance  not  only  sets  up  a  counter-electromotive  force  in  the  line, 
which  reduces  the  voltage  delivered  to  it  by  generators  or  transformers, 
but  also  causes  a  larger  current  to  flow  in  the  line  than  is  indicated  by  the 
division  of  the  number  of  watts  delivered  to  it  by  the  virtual  voltage  of 
delivery.  The  amount  of  current  increase  depends  on  both  the  induct- 
ance of  the  line  itself  and  also  on  the  character  of  its  connected  apparatus. 
In  a  system  with  a  mixed  load  of  lamps  and  motors  there  is  quite  certain 
to  be  some  inductance,  but  it  is  very  hard  to  predetermine  its  exact 
amount.  Experience  with  such  systems  shows,  however,  that  the  in- 
crease of  line  current  due  to  inductance  is  often  not  above  five  and  usually 
less  than  ten  per  cent  of  the  current  that  would  flow  if  there  were  no 
inductance.  To  provide  for  the  flow  of  this  additional  current,  due  to 
inductance,  without  an  increase  of  the  loss  in  volts  because  of  ohmic  re- 
sistance, the  cross  section  of  the  line  conductors  must  be  enlarged  by  a 
percentage  equal  to  that  of  the  additional  current.  This  means  that  in 


232     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

an  ordinary  case  of  a  transmission  with  either  single,  two,  or  three-phase 
alternating  current,  the  circular  mils  of  each  line  wire,  as  computed  with 
the  formulae  above  given,  should  be  increased  by  five  to  ten  per  cent. 
Such  increase  in  the  cross  section  of  wires  of  course  carries  with  it  a  like 
rise  in  the  total  weight  of  the  conductors  for  the  transmission.  If  wire  of 
the  cross  section  computed  with  the  formulae  is  employed  for  the  alternat- 
ing current  transmission,  inductance  in  an  ordinary  case  will  raise  the 
assumed  line  loss  of  power  by  five  to  ten  per  cent  of  what  it  would  be  if 
'no  inductance  existed.  Thus,  with  conductors  calculated  by  the  formulae 
for  a  power  loss  of  ten  per  cent  at  full  load,  inductance  in  an  ordinary 
case  would  raise  this  loss  to  somewhere  between  10.5  and  eleven  per 
cent.  As  a  rule  it  may  therefore  be  said  that  inductance  will  seldom  in- 
crease the  weight  of  line  conductors,  or  the  loss  of  power  therein,  by  more 
than  ten  per  cent. 

When  an  alternating  current  flows  along  a  conductor  its  density  is 
not  uniform  in  all  parts  of  each  cross  section,  but  the  current  density  is 
least  at  the  centre  of  the  conductor  and  increases  toward  the  outside 
surface.  This  unequal  distribution  of  the  alternating  current  over  each 
cross  section  of  a  conductor  through  which  it  is  passing  increases  with 
the  diameter  or  thickness  of  the  conductor  and  with  the  frequency  of 
the  alternating  current.  By  reason  of  this  action  the  ohmic  resistance 
of  any  conductor  is  somewhat  greater  for  an  alternating  than  for  a  con- 
tinuous current,  because  the  full  cross  section  of  the  conductor  cannot  be 
utilized  with  the  former  current.  Fortunately,  the  practical  importance 
of  this  unequal  distribution  of  alternating  current  over  each  cross  section 
of  its  conductor  is  usually  slight,  so  far  as  the  sizes  of  wires  for  transmis- 
sion lines  are  concerned,  because  the  usual  frequencies  of  current  and 
diameters  of  conductors  concerned  are  not  great  enough  to  give  the  effect 
mentioned  a  large  numerical  value.  Thus,  sixty  cycles  per  second  is  the 
highest  frequency  commonly  employed  for  the  current  on  transmission 
lines.  With  a  4-0  wire,  and  the  current  frequency  named,  the  increase 
in  the  ohmic  resistance  for  alternating  over  that  for  continuous  current 
does  not  reach  one-half  of  one  per  cent. 

Having  calculated  the  circular  mils  of  weight  of  a  transmission  line 
by  the  foregoing  formulae,  it  appears  that  the  only  material  increase  of 
this  weight  required  by  the  use  of  alternating  current  is  that  due  to 
inductance.  This  increase  cannot  be  calculated  exactly  beforehand  be- 
cause of  the  uncertain  elements  in  future  loads,  but  experience  shows 
that  it  is  seldom  more  than  ten  per  cent  of  the  calculated  size  or  weight 
of  conductors. 


CHAPTER  XVII, 

SELECTION  OF  TRANSMISSION  CIRCUITS. 

MAXIMUM  power,  voltage,  loss,  and  weight  of  conductors  having  been 
fixed  for  a  transmission  line,  the  number  of  circuits  that  shall  make  up 
the  line,  and  the  relations  of  these  circuits  to  each  other,  remain  to  be 
determined. 

In  practice  wide  differences  exist  as  to  the  number  and  relations  of 
circuits  on  a  single  transmission  line  between  two  points.  Cases  illus- 
trating this  fact  are  the  1 47-mile  transmission  from  Electra  power-house 
to  San  Francisco  and  the  65-mile  transmission  between  Canon  Ferry, 
on  the  Missouri  River  and  Butte,  Mont.  At  the  Electra  plant  the  gen- 
erator capacity  is  10,000  kilowatts,  and  the  transmission  to  San  Francisco 
is  carried  out  over  a  single  pole  line  that  carries  one  circuit  composed  of 
three  aluminum  conductors,  each  with  an  area  in  cross  section  of  471,000 
circular  mils.  From  the  generators  at  Canon  Ferry,  which  have  an 
aggregate  capacity  of  7,500  kilowatts,  a  part  of  the  energy  goes  to  Helena 
over  a  separate  line,  and  the  transmission  to  Butte  goes  over  two  pole 
lines  that  are  40  feet  apart.  Each  of  these  two  pole  lines  carries  a  single 
circuit  composed  of  three  copper  conductors,  and  each  conductor  has  a 
cross  section  of  105,600  circular  mils.  The  difference  in  practice  illus- 
trated by  these  two  plants  is  further  brought  out  by  the  fact  that  their 
voltages  are  not  far  apart,  as  the  Canon  Ferry  and  Butte  line  operates  at 
50,000,  and  the  Electra  and  San  Francisco  line  at  60,000  volts. 

Economy  in  the  construction  of  a  transmission  line  points  strongly  to 
the  use  of  a  single  circuit,  because  this  means  only  one  line  of  poles, 
usually  but  one  cross-arm  for  the  power  wires  per  pole,  the  least  possible 
number  of  pins  and  insulators,  and  the  smallest  amount  of  labor  for  the 
erection  of  the  conductors.  In  favor  of  a  single  circuit  there  is  also  the 
argument  of  greatest  mechanical  strength  in  each  conductor,  since  the 
single  circuit  is  to  have  the  same  weight  as  that  of  all  the  circuits  that 
may  be  adopted  in  its  place.  Where  each  conductor  of  the  single  circuit 
would  have  a  cross  section  of  less  than  83,690  circular  mils,  if  of  copper, 
corresponding  to  a  No.  i  B.  &  S.  gauge  wire,  the  argument  as  to  me- 
chanical strength  is  of  especial  force,  since  two  equal  circuits  instead  of 

233 


234     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

one,  in  the  case  where  one  circuit  of  No.  i  wires  would  have  the  required 
weight,  reduce  the  size  of  each  conductor  to  No.  4  wire,  of  41,740  circular 
mils  cross  section,  and  this  is  the  smallest  wire  that  it  is  practicable  to 
use  on  long  lines  for  mechanical  reasons.  Opposed  to  these  arguments 
for  a  single  circuit  are  those  based  on  the  supposed  greater  reliability  of 
two  or  more  circuits,  their  greater  ease  of  repair,  their  more  effective 
means  of  regulation,  and  the  influence  on  inductance  of  a  reduction  in 
the  size  of  conductors. 

In  spite  of  the  consequent  reduction  in  the  size  of  each  conductor, 
the  use  of  two  or  more  separate  circuits  for  the  same  transmission  is 
sometimes  thought  to  increase  its  reliability,  because  in  case  of  a  break 
or  short-circuit  on  one  of  the  circuits  the  other  will  still  be  available. 
Breaks  in  transmission  conductors  are  due  either  to  mechanical  strains 
alone,  as  wind  pressure,  the  falling  of  trees,  or  the  accumulation  of  ice, 
or  else  to  an  arc  between  the  conductors  that  tends  to  melt  them  at  some 
point.  As  a  smaller  conductor  breaks  or  melts  more  readily  than  a  large 
one,  the  use  of  two  or  more  circuits  instead  of  a  single  circuit  tends  to 
increase  troubles  of  this  sort.  It  thus  seems  that  while  two  or  more  cir- 
cuits give  a  greater  chance  of  continued  operation  after  a  break  in  a  con- 
ductor actually  occurs,  the  use  of  a  single  circuit  with  larger  conductors 
makes  any  break  less  probable. 

When  repairs  must  be  made  on  a  transmission  line,  as  in  replacing 
a  broken  insulator  or  setting  a  pole  in  the  place  of  one  that  has  burned, 
it  is  certainly  convenient  to  have  two  or  more  circuits  so  that  one  may 
be  out  of  use  while  the  repairs  on  it  are  made.  It  is  practicable,  however, 
to  make  such  repairs  on  any  high-voltage  circuit,  even  when  it  is  in  use, 
provided  the  conductors  are  spaced  so  far  apart  that  there  is  no  chance 
of  making  a  contact  or  starting  an  arc  between  them.  To  get  such  dis- 
tance between  conductors  there  should  be  only  one  circuit  per  pole,  and 
even  then  more  room  should  be  provided  for  that  circuit  than  is  common 
in  this  type  of  construction.  On  each  of  the  two  pole  lines  between 
Canon  Ferry  and  Butte  there  is  a  single  circuit  of  three  conductors 
arranged  in  triangular  form,  two  at  the  opposite  ends  of  a  cross-arm  and 
one  at  the  top  of  the  pole,  and  the  distance  from  each  conductor  of  a 
circuit  to  either  of  the  other  two  is  6.5  feet.  This  distance  between  con- 
ductors is  perhaps  as  great  as  that  on  any  transmission  circuit  now  in 
use,  but  it  seems  too  small  to  make  repairs  on  the  circuit  reasonably  safe 
when  it  is  in  operation  at  a  pressure  of  50,000  volts.  There  seems  to  be 
no  good  reason  why  the  distance  between  the  conductors  of  a  single 
circuit  to  which  a  pole  line  is  devoted  might  not  be  increased  to  as  much 


SELECTION  OF  TRANSMISSION  CIRCUITS.         235 

as  ten  feet,  at  the  slightly  greater  expense  of  longer  cross-arms.  With 
as  much  as  ten  feet  between  conductors,  and  special  tools  with  long 
wooden  handles  to  grasp  these  conductors,  there  should  be  no  serious 
danger  about  the  repair  of  even  6o,ooo-volt  lines  when  in  operation.  As 
the  6o,ooo-volt  line  between  Electra  and  San  Francisco  consists  of  only 
one  circuit,  it  seems  that  repairs  on  it  must  be  contemplated  during 
operation. 

Another  example  of  a  high-voltage  transmission  carried  out  with  a 
single  circuit  is  that  between  Shawinigan  Falls  and  Montreal,  a  distance 
of  eighty-five  miles.  In  this  case  the  circuit  is  made  up  of  three  alumi- 
num conductors,  each  of  which  has  an  area  in  cross  section  of  183,750 
circular  mils,  and  these  conductors  are  located  five  feet  apart,  one  at  the 
top  of  each  pole,  and  two  at  the  ends  of  a  cross-arm  below.  This  single 
circuit  is  in  regular  operation  at  50,000  volts  for  the  supply  of  light  and 
power  in  Montreal,  and  it  is  hard  to  see  how  repairs  while  there  is 
current  on  the  line  are  to  be  avoided. 

Inductance  varies  with  the  ratio  between  the  diameter  of  the  wires 
in  any  circuit  and  the  distance  between  these  wires,  but  as  inductance 
simply  raises  the  voltage  that  must  be  delivered  by  generators  or  trans- 
formers, and  does  not  represent  a  loss  of  energy,  it  may  generally  be 
given  but  little  weight  in  selecting  the  number  of  circuits,  the  distance  be- 
tween conductors,  and  the  size  of  each  conductor.  If  two  or  more  circuits 
with  smaller  conductors  have  a  combined  resistance  in  multiple  equal  to 
that  of  a  single  circuit  with  larger  conductors,  the  loss  of  voltage  due  to  in- 
ductance may  be  greater  on  the  single  circuit  than  the  corresponding  loss 
on  the  multiple  circuits,  but  the  advantages  due  to  the  single  circuit  may 
more  than  compensate  for  the  higher  pressure  at  generators  or  trans- 
formers. That  such  advantages  have  been  thought  to  exist  in  actual 
construction  may  be  seen  from  the  fact  that  the  1 4 7 -mile  line  from 
Electra  power-house  to  San  Francisco,  and  the  83 -mile  line  from  Sha- 
winigan Falls  to  Montreal,  are  composed  of  one  circuit  each.  As  induc- 
tance increases  directly  with  the  length  of  circuits,  these  very  long  lines 
are  especially  subject  to  its  influence,  yet  it  was  thought  that  the  advan- 
tages of  a  single  circuit  more  than  offset  its  disadvantages  in  each  case. 

Where  several  sub-stations,  widely  separated,  are  to  be  supplied  with 
energy  by  the  same  transmission  line,  another  argument  exists  for  the 
division  of  the  line  conductors  into  more  than  one  circuit,  so  that  there 
may  be  an  independent  circuit  to  each  sub-station.  As  the  pressure  for 
local  distribution  lines  must  be  regulated  at  each  sub-station,  it  is  quite 
an  advantage  to  have  a  separate  transmission  circuit  between  each  sub- 


236    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

station  and  the  power  plant,  so  that  the  voltage  on  each  circuit  at  the 
power-house  may  be  adjusted  as  nearly  as  possible  to  the  requirements 
of  its  sub-station.  An  interesting  illustration  of  this  practice  may  be 
noted  in  the  de'sign  of  transmission  circuits  for  the  line  between  Spier 
Falls  on  the  Hudson  River  and  the  cities  of  Schenectady,  Troy,  and 
Albany,  located  between  thirty  and  forty  miles  to  the  south,  which  passes 
through  Saratoga  and  Ballston  on  the  way.  When  this  transmission  line 
is  completed,  four  three-phase  circuits,  one  of  No.  o  and  three  of  No.  ooo 
copper  wire,  will  run  to  the  Saratoga  switch-house  from  the  generating 
plant  at  the  Falls,  a  distance  of  some  eight  miles. 

From  this  switch-house  two  circuits  of  No.  o  conductors  go  to  the 
Saratoga  sub-station,  a  little  more  than  one  mile  away,  two  circuits  of 
No.  ooo  wires  run  to  the  Watervliet  sub-station,  across  the  river  from 
Troy  and  thirty-five  miles  from  the  generating  station,  and  one  circuit 
of  No.  o  and  one  circuit  of  No.  ooo  wires  are  carried  to  Schenectady, 
thirty  miles  from  Spier  Falls,  passing  through  and  supplying  the  Ballston 
sub-station  on  the  way.  Other  circuits  connect  the  sub-station  at  Water- 
vliet with  that  at  Schenectady  and  with  the  water-power  station  at 
Mechanicsville.  From  the  Watervliet  sub-station  secondary  lines  run  to 
sub-stations  that  control  the  local  distribution  of  light  and  power  in 
Albany  and  Troy.  This  network  of  transmission  circuits  was  made 
desirable  by  the  conditions  of  this  case,  which  include  the  general  supply 
of  light  and  power  in  three  large  and  several  smaller  cities,  the  operation 
of  three  large  electric  railway  systems,  and  the  delivery  of  thousands  of 
horse-power  for  the  motors  in  a  great  manufacturing  plant. 

In  not  every  transmission  system  with  different  and  widely  scattered 
loads  it  is  thought  desirable  to  provide  more  than  one  main  circuit. 
Thus,  the  single  circuit  eighty-three  miles  long  that  transmits  energy 
from  Shawinigan  Falls  to  Montreal  is  designed  to  supply  power  also  in 
some  smaller  places  on  the  way. 

So  again,  the  1 47-mile  circuit  from  Electra  power-house  to  San  Fran- 
cisco passes  through  a  dozen  or  more  smaller  places,  including  Stockton, 
and  is  tapped  with  side  lines  that  run  to  Oakland  and  San  Jose.  In  cases 
like  this,  where  very  long  lines  run  through  large  numbers  of  cities  and 
towns  that  sooner  or  later  require  service,  it  is  obviously  impracticable 
to  provide  a  separate  circuit  for  each  centre  of  local  distribution.  It  may 
well  be  in  such  a  case  that  a  single  main  transmission  circuit  connected 
to  a  long  line  of  sub-stations  will  represent  the  best  possible  solution  of 
the  problem.  At  the  power-house  end  of  such  a  circuit  the  voltage  will 
naturally  be  regulated  to  suit  that  sub-station  where  the  load  is  the  most 


SELECTION  OF  TRANSMISSION  CIRCUITS. 


237 


important  or  exacting,  and  each  of  the  other  sub-stations  will  be  left  to 
do  all  of  the  regulating  for  its  own  load. 

The  greater  the  total  loss  of  voltage  on  a  transmission  line  supplying 
sub-stations  that  are  scattered  along  much  of  its  length,  the  larger  will 
be  the  fluctuations  of  voltage  that  must  be  compensated  for  at  all  of  the 
sub-stations  save  one,  under  changing  loads,  if  only  one  circuit  is  em- 
ployed between  the  power-plant  and  these  sub-stations.  Suppose,  for 
example,  that  a  transmission  line  100  miles  long  is  composed  of  a  single 
circuit,  and  supplies  two  sub-stations,  one  located  50  miles  and  the  other 


1, 1. 1: 


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s 

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. 

t     t 
a    ft 

—o^cv. 

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r3 

La    qj    13 13        w  q    q    m    un 

3   rl  fl  11      II  il   rl   a  ii 

FIG.  76.— Connections  at  Watervliet  Sub-station  on  Spier  Falls  Line. 

ioo  miles  from  the  power-plant.  Assume  at  first  that  there  is  no  load 
whatever  at  the  intermediate  sub-station.  If  the  single  transmission  cir- 
cuit operates  with  50,000  volts  at  the  power-plant,  and  45,000  volts  at 
the  sub-station  ioo  miles  away  when  there  is  a  full  load  there,  correspond- 
ing to  a  loss  of  ten  per  cent,  then  the  pressure  at  the  intermediate  sub- 
station will  be  47,500  volts.  If,  now,  the  load  at  the  sub-station  ioo 
miles  from  the  power-house  drops  to  a  point  where  the  entire  line  loss 
is  only  1,000  volts,  and  the  pressure  at  the  generating  plant  is  lowered 
to  46,000  volts  so  as  to  maintain  45,000  volts  at  the  more  distant  sub- 
station, then  the  pressure  at  the  intermediate  sub-station  will  be  45,500 
volts,  or  2,000  volts  less  than  it  was  before.  If  the  loss  on  the  entire  line 
at  full  load  were  only  five  per  cent,  making  the  voltage  at  the  sub-station 
ioo  miles  away  47^,500  when  that  at  the  generating  station  is  50,000, 


238     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

then  the  pressure  at  the  intermediate  sub-station  will  be  48,750  volts. 
Upon  a  reduction  of  the  loss  on  the  entire  length  of  line  to  one-fifth  of 
its  maximum  amount,  or  to  500  volts,  the  pressure  at  the  generating  sta- 
tion must  be  reduced  to  48,000  volts,  if  that  at  the  more  distant  sub- 
station is  to  be  held  constant  at  47,500.  At  the  intermediate  sub-station 
the  pressure  will  then  be  47,750  volts,  or  1,000  volts  less  than  it  was  at 
full  load.  From  these  two  examples  it  may  be  seen  that  the  extent  of 
pressure  variation  at  the  intermediate  sub-station  will  depend  directly 


FIG.  77.— Sections  of  Switch-house  on  New  Hampshire  Traction  System. 

on  the  maximum  line  loss,  if  the  regulation  at  the  generating  station  is 
such  as  to  maintain  a  constant  voltage  at  the  sub-station  100  miles  away. 

All  the  foregoing  has  assumed  no  load  to  be  connected  at  the  inter- 
mediate sub-station,  and  with  a  load  there  the  fluctuations  of  pressure 
will  of  course  depend  on  its  amount  as  well  as  on  the  load  at  the  more 
distant  sub-station. 

One  of  the  strongest  reasons  for  the  use  of  two  or  more  circuits  in 
the  same  transmission  line  arises  from  the  rapid  fluctuations  of  load 
where  large  stationary  motors  or  an  electric  railway  system  is  operated. 
When  a  transmission  line  must  carry  a  load  of  stationary  or  railway 
motors,  it  is  a  common  practice  to  divide  the  line  into  at  least  two  cir- 


SELECTION  OF  TRANSMISSION  CIRCUITS.         239 

» 

cuits,  and  to  devote  one  circuit  exclusively  to  railway  or  motor  work 
and  another  to  lighting,  at  any  one  time.  In  some  cases  this  division 
of  the  transmission  system  into  two  parts,  one  devoted  to  the  lighting 
and  the  other  to  the  motor  load,  is  carried  out  not  only  as  to  the  sub- 
station apparatus  and  the  line,  but  also  as  to  the  transformers,  genera- 
tors, water-wheels,  and  even  the  penstocks  at  the  power-plant.  It  is 
possible  even  to  carry  this  division  of  the  transmission  system  still  fur- 
ther, and  to  separate  either  the  motor  or  the  lighting  load,  or  both,  into 
sections,  and  then  to  devote  a  distinct  transmission  circuit,  group  of 
transformers,  generator,  and  water-wheel  to  the  operation  of  each  sec- 
tion. An  example  of  the  complete  division  of  generating  and  transmit- 
ting apparatus  into  independent  units  may  be  noted  in  the  case  of  the 
system  that  supplies  light  and  power  in  Portland,  Me.,  from  a  generating 
plant  on  the  Presumpscot  River,  thirteen  miles  away.  At  this  station 
four  steel  penstocks,  each  provided  with  a  separate  gate  at  the  forebay 
wall,  bring  water  to  as  many  pairs  of  wheels,  and  each  pair  of  wheels 
drives  a  direct-connected  generator.  Four  three-phase  circuits  connect 
the  generating  plant  with  the  sub-station  at  Portland,  and  each  circuit 
between  the  generating  plant  and  a  transformer-house  outside  the  busi- 
ness section  of  the  city  is  made  up  of  No.  2  solid  soft-drawn  copper 
wires. 

Each  of  these  four  sets  of  apparatus,  from  head-gate  to  sub-station, 
is  usually  operated  independently  of  the  others,  and  supplies  either  the 
motor  load  or  a  part  of  the  electric  lighting.  In  this  way  changes  in  the 
amount  of  one  section  of  the  load  cause  no  fluctuation  of  the  voltage 
on  the  other  sections.  At  Manchester,  N.  H.,  the  sub-station  receives 
energy  from  four  water-power  plants,  and  is  provided  with  two  sets  of 
low-tension,  2,3oo-volt,  three-phase  bus-bars,  one  set  of  these  bus-bars 
being  devoted  to  the  operation  of  the  local  electric  railway  system,  and 
the  other  set  to  the  supply  of  lamps  and  stationary  motors.  Each  set 
of  these  bus-bars  is  divided  into  a  number  of  sections,  and  by  means  of 
these  sections  different  transmission  circuits  are  devoted  to  different 
portions  of  the  lighting  and  motor  loads.  As  three  of  the  four  water- 
power  plants  are  connected  to  the  sub-station  by  two  circuits  each,  the 
division  of  loads  in  this  case  is  often  carried  clear  back  to  the  generators, 
one  generator  in  a  power-house  being  operated,  for  instance,  on  railway 
work  and  another  on  a  lighting  load  at  the  same  time.  This  plan  has 
the  obvious  advantage  that  much  of  the  regulation  for  the  several  parts 
of  the  entire  load  may  be  done  at  the  generators,  thus  reducing  the 
amount  of  regulation  necessary  at  the  sub-station,  and  that  fluctuat- 


240    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

« 
ing  motor  loads  do  not  affect  the  lamps.     In  this  case  the  conductors 

of  the  several  transmission  circuits  are  all  of  moderate  size,  and  the 
division  of  the  lines  was  evidently  adopted  for  purposes  of  regulation, 
rather  than  to  reduce  the  amount  of  inductance.  Thus  the  line  between 
Gregg's  Falls  and  the  sub-station,  a  distance  of  six  miles,  is  made  up  of 
one  three-phase  circuit  of  No.  4  and  one  circuit  of  No.  6  bare  copper 
wires.  The  fourteen-mile  line  between  the  plant  at  Garvin's  Falls  and 
the  sub-station,  the  longest  of  the  four  transmissions,  is  made  up  of  two 
three-phase  circuits,  each  composed  of  No.  o  bare  copper  wires.  In  the 
case  of  the  Gregg's  Falls  plant  the  subdivision  of  the  line  has  gone  further 
than  that  of  the  generating  equipment,  for  the  station  there  contains  only 
a  single  generator,  the  rating  being  1,200  kilowatts,  while  two  circuits 
run  thence  to  the  sub-station.  Another  instance  showing  extensive  sub- 
division of  a  line  into  separate  circuits  may  be  noted  in  the  seven-mile 
transmission  from  Montmorency  Falls  to  Quebec,  Canada,  where  six- 
teen conductors,  each  No.  o  copper  wire,  make  up  four  two-phase  cir- 
cuits that  connect  a  plant  of  2,400  kilowatts  capacity  with  its  sub-station. 
Such  multiplication  of  transmission  circuits  has  some  advantages  from 
the  standpoint  of  regulation,  but  there  are  good  reasons  for  limiting  it 
to  rather  short  lines,  where  it  is,  in  fact,  almost  exclusively  found.  On 
very  long  lines  the  use  of  numerous  circuits  composed  of  rather  small 
conductors  would  obviously  increase  the  constant  expense  of  inspection 
and  repairs  and  add  materially  to  uncertainty  of  the  service.  Very  few, 
if  any,  transmission  lines  of  as  much  as  twenty-five  miles  in  length  are 
divided  into  more  than  two  circuits,  and  in  several  instances  lines  of 
superlative  length  have  only  a  single  circuit  each.  The  greatest  single 
power  transmission  in  the  world,  that  between  Niagara  Falls  and  Buffalo, 
is  carried  out  with  two  pole  lines,  one  of  which  is  about  twenty  and  the 
other  about  twenty-three  miles  long.  The  longer  pole  line,  which  is  also 
the  older,  carries  two  three-phase  circuits,  each  of  which  is  made  up  of 
three  350,000  circular  mil  copper  conductors.  The  shorter  pole  line 
carries  a  single  three-phase  circuit  composed  of  aluminum  conductors, 
each  of  which  has  an  area  in  cross  section  of  500,000  circular  mils.  In 
electrical  conductivity  the  aluminum  circuit  is  intended  to  be  equal  to 
each  of  the  two  that  are  composed  of  copper.  According  to  the  descrip- 
tion of  the  Niagara  Falls  and  Buffalo  transmission  system  in  vol.  xviii., 
A.  I.  E.  E.,  pages  518  to  527,  each  of  these  three  circuits  is  designed  to 
transmit  about  7,500  kilowatts,  and  the  maximum  power  transmitted  up 
to  August,  1901,  was  15,600  kilowatts,  or  about  the  calculated  capacity 
of  two  of  the  circuits.  According  to  the  description  just  mentioned,  the 


SELECTION  OF  TRANSMISSION  CIRCUITS.         241 

transmission  circuits  used  to  supply  energy  for  use  at  Buffalo  are  regu- 
larly operated  in  parallel,  and  this  is  also  true  of  the  generators  and  the 
step-down  transformers,  though  the  uses  to  which  this  energy  is  applied 
include  lighting,  large  stationary  motors,  and  the  electric  railway  system. 
Apparatus  in  the  generating  station  at  Niagara  Falls  and  in  the  terminal- 
house  near  the  city  limits  of  Buffalo  is  so  arranged,  however,  that  two 
of  the  3,750  kilowatt  generators  and  eight  step-up  transformers  at  the 
power-house,  together  with  one  transmission  circuit  and  three  step-down 
transformers  in  the  terminal-house  at  Buffalo,  may  be  operated  inde- 
pendently of  all  the  other  apparatus. 

As  already  pointed  out,  the  use  of  separate  circuits  for  each  sub- 
station, and  for  lighting  and  power  loads  at  each  sub-station  in  very  long 
transmission  systems,  is  often  impracticable.  Even  in  comparatively  short 
transmissions  the  multiplication  of  circuits  and  the  use  of  rather  small 
and  mechanically  weak  conductors  increased  the  first  cost  of  installation 
and  the  subsequent  expense  of  inspection  and  repairs.  An  objection  to 
operation  with  a  single  circuit  in  a  transmission  line  that  supplies  widely 
separated  sub-stations  with  lighting,  power,  and  railway  loads  is  the 
consequent  difficulty  of  pressure  regulation  on  the  distribution  lines  at 
each  sub-station.  Such  a  transmission  line  necessarily  delivers  energy 
at  different  and  fluctuating  voltages  at  the  several  sub-stati  3ns,  and 
these  fluctuations  are  of  course  reproduced  on  the  secondary  side  of 
the  step-down  transformers.  Fortunately,  however,  the  use  of  syn- 
chronous motor  generators,  either  in  place  of  or  in  connection  with  static 
transformers,  goes  far  to  solve  the  problem  of  pressure  regulation  for  dis- 
tribution circuits  supplied  with  energy  from  transmission  lines.  This  is 
due  to  the  well-known  fact  that  with  constant  frequency  the  speed  of  rota- 
tion for  a  synchronous  motor  is  constant  without  regard  to  fluctuations  in 
the  applied  voltage  or  changes  in  its  load.  With  a  constant  speed  at  the 
motor  and  its  connected  generator  it  is  of  course  easy  to  deliver  current 
at  constant  voltage  to  the  distribution  lines.  This  constancy  of  speed 
makes  the  synchronous  motor  generator  a  favorite  in  large  transmission 
systems  with  both  power  and  lighting  loads.  The  satisfactory  lighting 
service  in  Buffalo,  operated  with  energy  transmitted  from  Niagara  Falls, 
seems  to  be  due  in  some  measure  to  the  use  of  synchronous  motor  gen- 
erators at  the  sub-station  in  Buffalo,  whence  lighting  circuits  are  sup- 
plied. As  above  stated,  the  three  circuits  that  make  up  the  transmission 
line  between  Niagara  Falls  and  Buffalo  are  operated  in  multiple,  and  in 
the  latter  place  there  is  a  large  load  of  both  railway  and  stationary  motors. 
As  the  three  circuits  are  operated  in  multiple,  they  of  course  amount  to 
16 


242     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

only  a  single  circuit  so  far  as  fluctuations  of  voltage  due  to  changes  in 
these  several  sorts  of  loads  are  concerned.  According  to  vol.  xviii.,  A.  I. 
E.  E.,  pages  125  and  following,  the  load  on  the  transmission  system  at 
Buffalo  in  1901  was  made  up  of  about  7,000  horse-power  in  railway 
motors,  4,000  horse-power  in  induction  motors,  and  4,000  horse-power 
divided  up  between  series  arc  lamps,  constant  pressure  incandescent 
lamps,  and  continuous  current  motors.  The  railway  load  is  operated 
through  step-down  transformers  and  rotary  converters.  The  induction 
motors  are  connected  either  to  the  2,000- volt  secondary  circuits  of  the 
step-down  transformers  or  to  service  transformers  supplied  by  these 
circuits.  On  these  railway  and  stationary  motor  loads  there  is  of  course 
no  necessity  for  close  pressure  regulation.  Series  arc  lamps  are  operated 
through  step-down  transformers  and  synchronous  motors  direct-con- 
nected to  constant  continuous  current  dynamos.  Continuous  current 
stationary  motors  draw  power  from  the  transmission  lines  through  step- 
down  transformers  and  rotary  converters,  like  the  railway  load.  For  the 
2,200  volt  circuits  that  supply  service  transformers  for  commercial  arc  and 
incandescent  lighting  the  transmitted  energy  passes  through  step-down 
transformers  and  synchronous  motor-generators.  These  motor-genera- 
tors raise  the  frequency  from  twenty-five  to  sixty  cycles  per  second. 
Finally  the  continuous  current  three-wire  system  for  incandescent  light- 
ing at  about  250  volts  between  outside  wires  is  operated  through  step- 
down  transformers  and  synchronous  motors  direct-connected  to  continu- 
ous current  generators.  For  this  last-named  service  rotary  converters 
were  at  first  tried,  but  were  found  to  be  impracticable  because  voltage 
fluctuations  on  the  transmission  line  (due  largely  to  the  railway  and 
motor  loads)  were  reproduced  on  the  continuous-current  circuits  by  the 
rotary  converters.  Since  the  adoption  of  motor-generators  this  fluctua- 
tion of  the  service  voltage  is  no  longer  present. 

Another  case  in  which  synchronous  motor-generators  deliver  power 
from  a  transmission  line  that  carries  both  a  lighting  and  a  motor  load 
is  that  of  the  Shawinigan  sub-station  in  Montreal.  At  this  sub-station 
the  85-mile  transmission  line  from  the  generating  plant  at  Shawinigan 
Falls  terminates.  As  already  pointed  out,  this  line  is  composed  of  a 
single  three-phase  circuit  of  aluminum  conductors,  each  of  .which  has  a 
cross  section  of  183,750  circular  mils.  In  the  Montreal  sub-station  the 
thirty-cycle,  three-phase  current  from  Shawinigan  Falls  is  delivered  to 
transformers  that  lower  the  voltage  to  2,300.  The  current  then  goes  to 
five  synchronous  motor-generators  of  1,200  horse-power  capacity  each, 
and  is  there  converted  to  sixty-three  cycles  per  second,  two-phase,  at  the 


SELECTION  OF  TRANSMISSION  CIRCUITS.         243 

same  voltage.  This  converted  current  passes  onto  the  distribution  lines 
of  the  local  electrical  supply  system  in  Montreal,  which  also  draws  energy 
from  two  other  water-power  plants,  and  is  devoted  to  lighting,  stationary 
motors,  or  to  the  street  railway  work,  as  may  be  required.  Though  sep- 
arate local  distribution  circuits  are  devoted  to  these  several  loads,  the 
fluctuations  in  the  stationary  and  railway  motor  work  necessarily  react 
on  the  voltage  of  the  transmission  line  and  transformers  at  the  sub-station. 
By  the  use  of  the  synchronous  motor-generators  the  lighting  circuits  are 
protected  from  these  pressure  variations. 

As  the  numbers  of  sub-stations  at  different  points  on  long  transmis- 
sion lines  increase,  and  stationary  motor  and  railway  loads  at  each  be- 


Power  tine 


\Y\\\\\\\\\ 


FIG.  78.— Transfer  Switches  at  Saratoga  Switch-house  on  Spier  Falls  Line. 

come  more  common,  it  is  to  be  expected  that  the  use  of  synchronous 
motor-generators  for  lighting  service  will  be  much  more  frequent  than 
at  present.  With  such  use  there  will  disappear  one  of  the  reasons  for 
the  multiplication  of  transmission  circuits. 

Where  several  transmission  circuits  connect  a  generating  plant  with 
a  single  sub-station,  or  with  several  sub-stations  in  the  same  general 
direction,  it  is  desirable  to  have  switches  so  arranged  that  two  or  more 
circuits  may  be  combined  as  one,  or  so  that  any  circuit  that  ordinarily 
operates  a  certain  load  or  sub-station  may  be  devoted  to  another  when 
occasion  requires.  For  this  purpose  transfer  switches  on  each  circuit 


244     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

are  necessary  at  generating  plants,  sub-stations,  and  often  at  switch- 
houses.  These  transfer  switches  will  ordinarily  be  of  the  knife  type, 
and  intended  for  manual  operation  when  the  circuits  to  which  they 
are  connected  are  not  in  use.  As  such  switches  are  exposed  to  the  full 
voltage  of  transmission,  the  insulation  of  their  conducting  parts  should 
be  very  high.  In  the  extensive  transmission  system  between  the  power- 
plants  at  Spier  Falls  and  Mechanicsville  and  the  sub-stations  at  Troy, 
Albany,  and  Schenectady,  N.  Y.,  a  transfer  switch  of  highly  insulated 
construction  has  been  much  used.  The  two  blades  of  this  switch  move 
independently  of  each  other,  but  both  are  mounted  between  the  same 


FIG.  79.— Cross  Section  of  Schenectady  Switch-house  on  Spier  Falls  Line. 

metal  clips.  Each  blade  is  of  two  by  one-quarter  inch  drawn  copper 
rod,  and  the  clips  supporting  the  two  blades  are  mounted  on  top  of  a 
circular  metal  cap  four  and  three-quarter  inches  in  outside  diameter  and 
two  inches  high,  that  is  cemented  over  the  top  of  a  large,  double  petti- 
coat, porcelain  line  insulator. 

Clips  into  which  these  copper  blades  are  swung  in  closing  the  switch 
are  also  mounted  in  caps  carried  by  insulators  in  the  way  just  described. 
Each  of  these  insulators  is  mounted  on  a  large  wooden  pin,  and  these  pins 
are  secured  in  timbers  at  the  points  where  the  switches  are  wanted. 
This  construction  of  switches  gives  ample  insulation  for  the  line  voltage 


SELECTION  OF  TRANSMISSION  CIRCUITS. 


245 


of  30,000  in  this  system.  By  means  of  the  transfer  switches  just  de- 
scribed, either  of  the  transmission  circuits  leaving  the  Spier  Falls  power- 
plant  may  be  connected  to  any  one  of  the  ten  generators  and  ten  groups 
of  transformers  there.  At  the  Saratoga  switch-house,  any  one  of  the 
twelve  conductors,  making  up  the  four  three-phase  circuits  from  Spier 
Falls  may  be  connected  to  any  one  of  the  eighteen  conductors  making 
up  the  six  three-phase  circuits  that  go  south  to  Saratoga,  Watervliet,  and 
Schenectady  sub-stations,  in  the  way  indicated  by  the  drawing.  So 
again  at  the  Watervliet  sub-station,  where  energy  at  26,500  volts  is  re- 
ceived from  Spier  Falls  and  energy  at  10,800  volts  from  Mechanicsville, 
any  single  conductor  from  either  of  these  water-power  plants  may  be 
connected,  either  directly  or  through  a  transformer,  with  either  conductor 
running  to  the  railway  and  lighting  sub-stations  about  Albany  and  Troy. 
Where  several  transmission  circuits  are  employed,  this  complete  flexibility 
of  connection  evidently  adds  materially  to  the  convenience  and  reliability 
of  operation. 

CIRCUITS  IN  TRANSMISSION  LINES. 


.2 

5s 

jj| 

i-Sui 

It 

%** 

Location  of  Lines. 

|a 

J5  3 
B| 

ly 

111 

111 

J 

fc« 

6^^ 

UC« 

Electra  to  San  Francisco  

147 

I 

J 

*47l  0^4 

60 

Colgate  to  Oakland  Cal 

J42 

2       < 

2 

' 

60 

*2  1  1  ,000 

Santa  Ana  River  to  Los  Angeles  

^ 

2 

83,690 

60 

Shawinigan  Falls  to  Montreal  

85 

I 

3° 

Caiion  Ferry  to  Butte 

fio 

Welland  Canal  to  Hamilton 

?r 

I 

87     6OO 

60 

Welland  Canal  to  Hamilton  . 

•77 

c\5>uyu 

60 

Spier  Falls  to  Schenectadv  .  .  . 

2 

3 

167,800 

Spier  Falls  to  Wratervliet,  N.  Y.  ... 

35 

2 

167,800 

40 

Ogden  to  Salt  Lake  City  

36 

2 

87  600 

60 

Apple  River  Falls  to  St.  Paul  

27 

2 

66  370 

60 

Niagara  Falls  to  Buffalo  

27, 

2 

7CO  OOO 

2  ? 

Niagara  Falls  to  Buffalo  . 

2O 

Farmington  River  to  Hartford  

II 

I 

60 

Niagara  Falls  to  Toronto.  .    . 

7$ 

2 

j  + 

25 

*  Aluminum  "conductor. 


t  Steel  towers. 


CHAPTER  XVIII. 

POLE  LINES  FOR  POWER  TRANSMISSION. 

LONG  transmission  lines  should  follow  the  most  direct  routes  between 
generating  and  sub-stations  as  far  as  practicable.  The  number  of  poles, 
cross-arms,  and  insulators  increases  directly  with  the  length  of  line,  and 
the  weight  of  conductors  with  the  square  of  that  length,  other  factors 
remaining  equal.  Every  material  deviation  from  a  straight  line  must 
therefore  be  paid  for  at  a  rather  high  rate. 

Distribution  lines  necessarily  follow  the  public  streets  in  order  to 
reach  consumers,  but  the  saving  of  the  cost  of  a  private  right  of  way  and 
ease  of  access  are  the  main  considerations  which  tend  to  keep  transmis- 
sion lines  on  streets  and  highways.  Except  in  very  rough  or  swampy 
country,  the  difficulty  of  access  to  a  pole  line  on  a  private  right  of  way  is 
not  a  serious  matter  and  should  be  given  but  little  weight.  The  cost  of 
a  private  right  of  way  may  be  more  important,  and  should  be  compared 
with  the  additional  cost  of  the  pole  line  and  conductors  if  erected  on  the 
public  highway.  In  this  additional  cost  should  be  included  any  items  for 
paving  about  the  poles,  extra  pins,  insulators,  and  guys  made  necessary 
by  frequent  turns  in  the  highway,  and  the  sums  that  may  be  required  to 
secure  the  necessary  franchises.  There  is  also  the  possible  contingency 
of  future  legislation  as  to  the  voltage  that  may  be  maintained  on  wires 
located  over  public  streets.  These  considerations  taken  together  give  a 
strong  tendency  to  the  location  of  long  transmission  lines  on  private  rights 
of  way,  especially  where  the  amount  of  power  involved  is  great  and  the 
voltage  very  high. 

A  transmission  line  80.3  miles  in  length  recently  erected  between 
Rochester  and  Pelham,  N.  H.,  by  way  of  Portsmouth,  where  the  gen- 
erating station  is  located,  to  feed  an  electric  railway  system,  operates 
at  13,200  volts  and  is  mainly  located  on  private  rights  of  way.  Deeds 
conveying  the  easements  for  this  right  of  way  provide  that  all  trees  or 
branches  within  one  rod  on  either  side  of  the  line  may  be  cut  away. 
The  transmission  line  between  Niagara  Falls  and  Buffalo,  about  twenty- 
three  miles  long  and  operating  at  22,000  volts,  is  largely  on  a  private 
way  thirty  feet  wide. 

246 


POLE  LINES  FOR  POWER  TRANSMISSION. 


247 


248     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

For  the  transmission  between  Canon  Ferry  and  Butte  the  line  is 
mainly  located  on  a  private  way.  Between  Colgate  and  Oakland  the 
transmission  line  is  mostly  on  private  way,  and  this  is  also  true  of  the 
greater  part  of  some  other  high-pressure  lines  in  California.  These  pri- 
vate rights  of  way  range  from  fifty  to  several  hundred  feet  wide,  it  being 
necessary  in  forests  to  cut  down  all  trees  that  are  tall  enough  to  fall  onto 
the  wires. 

In  some  cases  of  transmission  at  very  high  voltage  two  independ- 
ent pole  lines  are  erected  and  one  or  more  circuits  are  then  run  on  each 
set  of  poles.  This  construction  has  been  followed  on  the  transmission 
line  between  Niagara  Falls  and  Buffalo,  Canon  Ferry  and  Butte,  Welland 
Canal  and  Hamilton,  and  between  Colgate  and  Oakland.  Such  double 
pole  lines  are  more  usually  located  on  the  same  right  of  way,  this  being 
true  of  the  Canon  Ferry  and  Colgate  systems,  but  this  is  not  always  the 
case.  In  the  Hamilton  system  the  two  lines  of  poles,  one  thirty-five 
miles  and  the  other  thirty-seven  miles  in  length,  are  located  several 
miles  apart.  The  two  sets  of  poles  on  a  part  of  the  Buffalo  line  are 
less  than  thirty  feet,  on  the  Colgate  line  are  twenty-five  feet,  and  on  the 
Canon  Ferry  line  are  forty  feet  apart. 

The  main  reasons  for  the  use  of  two  pole  lines  instead  of  one  are  the 
probability  that  an  arc  started  on  one  circuit  will  be  communicated  to 
another  on  the  same  poles,  and  the  greater  ease  and  safety  of  repairs  when 
each  circuit  is  on  a  separate  line  of  poles.  On  each  pole  line  of  the  Canon 
Ferry  transmission,  and  also  on  each  pole  line  of  the  Colgate  transmission, 
there  is  only  one  three- wire  circuit.  On  the  Canon  Ferry  line  each  wire  of 
the  two  circuits  has  a  cross-section  of  only  106,500  circular  mils,  and  on 
the  Colgate  line  one  circuit  is  of  133,225  circular  mils  wire  and  the  other 
circuit  is  of  21 1 ,600  circular  mils  cable.  In  contrast  with  these  figures  the 
line  of  the  Standard  Electric  Company  between  Electra  and  Mission  San 
Jose,  a  distance  of  ninety-nine  miles,  is  made  up  of  only  three  conductors, 
each  being  an  aluminum  cable  of  471,034  circular  mils  section.  Induct- 
ance increases  with  the  frequency  of  the  current  in  a  conductor,  and  in 
each  of  the  three  systems  just  considered  the  frequency  is  sixty  cycles 
per  second. 

The  use  of  one  circuit  of  larger  wire  instead  of  two  circuits  of  smaller 
wire  has  the  obvious  advantage  of  greater  mechanical  strength  in  each 
conductor,  saves  the  cost  of  one  pole  line  and  of  the  erection  of  the  second 
circuit.  With  voltages  above  40,000  to  50,000  on  long  transmission  lines 
there  is  a  large  loss  of  energy  by  leakage  directly  through  the  air  from  wire 
to  wire.  To  keep  this  loss  within  desirable  limits  it  may  be  necessary  to 


POLE  LINES  FOR  POWER  TRANSMISSION. 


249 


give  each  wire  of  a  circuit  a  greater  distance  from  the  others  of  the  same 
circuit  than  can  readily  be  had  if  all  the  wires  of  each  circuit  are  mounted 
on  one  line  of  poles.  If  there  is  only  one  three- wire  circuit  to  be  provided 
for,  three  lines  of  poles  or  two  lines  with  a  long  crosspiece  between  them 
may  be  set  with  any  desired  distance  between  the  lines  so  that  the  leak- 
age through  the  air  with  one  wire  on  each  pole  will  be  reduced  to  a  small 
quantity.  On  a  line  built  in  this  way  it  would  be  practically  impossible 
for  an  arc  to  start  between  the  wares  by  any  of  the  usual  means. 

Distances  from  pole  to  pole  in  the  same  line  vary  somewhat  with  the 
number,  size,  and  material  of  the  conductors  to  be  carried.     On  ordinary 


FIG.  81.— Chambly-  Montreal  Line  Crossing  the  Chambly  Canal. 

construction  in  a  straight  line  poles  are  often  spaced  from  100  to  no  feet 
apart — that  is,  about  fifty  poles  per  mile.  On  curves  and  near  corners 
the  spacing  of  poles  should  be  shorter.  Poles  for  the  80.3  miles,  men- 
tioned in  New  Hampshire,  are  regularly  located  100  feet  apart.  Of  the 
two  pole  lines  between  Niagara  Falls  and  Buffalo,  the  older  was  de- 
signed to  carry  twelve  copper  cables  of  350,000  circular  mils  each,  and 
its  poles  were  spaced  only  70  feet  apart.  The  newer  line  is  designed  to 
carry  six  aluminum  cables  of  500,000  circular  mils  each  and  its  poles  are 
140  feet  apart.  Poles  in  each  of  the  lines  between  Canon  Ferry  and 
Butte  are  regularly  spaced  no  feet  apart  and  each  pole  carries  three 
copper  cables  of  106,500  circular  mils. 


250     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

The  two  142-mile  lines  between  Colgate  and  Oakland  are  each  made 
up  of  poles  132  feet  apart,  and  one  line  of  poles  carries  the  three  copper 
conductors  and  the  other  line  of  poles  the  aluminum  conductors  already 
named.  As  aluminum  wire  has  only  one-half  the  weight  of  copper 
wire  of  equal  conductivity,  the  length  of  span  between  poles  carrying 
aluminum  wire  may  be  greater  than  that  where  copper  is  used.  Only 
a  part  of  the  strain  on  poles  is  due  to  the  weight  of  wires  carried,  how- 
ever. Where  a  body  of  water  must  be  crossed,  a  very  long  span,  with 
special  supports  for  the  wires  at  each  side,  may  be  necessary.  A  case 


FIG.  82.— Special  Wooden  Structures  on  Line  Between  Spier  Falls  and  Schenectady. 

of  this  sort  was  met  where  the  Colgate  and  Oakland  line  crosses  the 
Carquinez  Straits  at  a  point  where  the  waterway  is  3,200  feet  wide.  It 
was  necessary  to  have  the  lowest  part  of  the  cables  across  these  straits  at 
least  200  feet  above  the  surface  of  the  water  so  that  vessels  with  the  tallest 
masts  could  pass  underneath.  To  secure  the  necessary  elevation  for  the 
cables  a  steel  tower  was  built  on  each  bank  of  the  straits  at  such  a  point 
that  the  distance  between  the  points  for  cable  support  on  the  two  towers 
is  4,427  feet  apart.  As  the  banks  rise  rapidly  from  the  water  level,  one 
steel  tower  was  given  a  height  of  only  65  feet,  while  the  height  of  the  other 
was  made  225  feet.  Between  these  two  towers  four  steel  cables  were 
suspended,  each  cable  being  made  up  of  nineteen  strands  of  galvanized 


POLE  LINES  FOR  POWER  TRANSMISSION.          251 


steel  wire,  having  an  outside  diameter  of  seven-eighths  inch  and  weighing 
7,080  pounds  for  the  span.  The  breaking  strain  of  each  cable  is  98,000 
pounds,  and  it  has  the  electrical  conductivity  of  a  No.  2  copper  wire. 
The  cables  are  simply  supported  on  the  towers  by  steel  rollers,  and  the 
pull  of  each  cable,  amounting  to  twelve  tons,  is  taken  by  an  anchorage 
some  distance  behind  each  tower,  where  the  cable  terminates.  Each 
anchorage  consists  of  a  large  block  of  cement  deeply  embedded  in  the 
ground,  and  with  anchor  bolts  running  through  it.  Each  cable  is  secured 
to  its  anchorage  through  a  series  of  strain  insulators,  and  the  regular  line 


Fio.  83.— Special  Structure  on  Line  Between  Spier  Falls  and  Schenectady. 

cables  of  copper  and  aluminum  are  connected  with  the  steel  cables  just 
outside  of  the  shelter  built  over  the  strain  insulators  of  each  anchor. 
Steel  cables  were  used  for  the  long  span  across  the  straits  because  of  the 
great  tensile  strength  that  could  be  had  in  that  metal.  This  span  is,  no 
doubt,  the  longest  and  highest  that  has  ever  been  erected  for  electrical 
transmission  at  high  voltage. 

It  has  been  suggested  in  one  instance  that  steel  towers  ninety  feet 
high  and  1,000  feet  apart  be  substituted  for  pole  lines  and  the  wires 
strung  from  tower  to  tower.  Such  construction  would  increase  the 
difficulty  of  insulation  and  would  cost  more  at  the  start  than  a  line  of 
wooden  poles.  The  question  is  whether  a  lower  maintenance  and 
depreciation  rate  for  the  steel  towers  would  offset  their  disadvantages 


252     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

compared  with  poles.  Pole  lines  should  be  staked  out  with  a  transit,  and 
the  same  instrument  can  be  used  to  give  a  perpendicular  position  to  each 
pole  and  bring  it  into  line.  Wooden  poles  are  used  in  most  cases  of 
high-voltage  transmission  lines.  Iron  poles  would  make  it  unsafe  to 
work  on  any  circuit  carried  by  them  when  it  was  transmitting  current 
at  high  voltage.  With  iron  poles  a  defective  insulator  might  lead  to 


FIG.  84.— Crossing  of  Delaware  and  Hudson  Railway  Tracks  by  30,ooo-volt  Line  at 

Saratoga,  N.  Y. 

the  destruction  of  the  conductors  at  that  point  through  continuous 
arcing  on  to  the  iron. 

The  kinds  of  wood  used  for  poles  vary  in  different  sections  of  the 
country.  In  New  England,  chestnut  poles  are  a  favorite  and  were  used 
on  the  80.3  miles  of  transmission  line  mentioned  in  New  Hampshire. 
Cedar  poles  are  used  to  some  extent  in  nearly  all  parts  of  the  country, 
including  Canada.  Spruce  and  pine  poles  are  employed  to  some  extent, . 
especially  in  lengths  of  more  than  fifty  feet.  In  the  Rocky  Mountain 
region  and  in  California  round  cedar  poles  from  the  forests  of  Oregon, 


POLE  LINES  FOR  POWER  TRANSMISSION.          253 

Washington,  and  Idaho  are  much  used.  Sawed  redwood  poles  from  the 
trunks  of  large  trees  were  erected  on  the  14 7-mile  line  between  Electra 
power-house  and  San  Francisco.  For  the  Colgate  and  Oakland  line 
Oregon  cedar  poles  were  selected,  and  the  transmission  between  Canon 
Ferry  and  Butte  was  carried  out  with  cedar  poles  from  Idaho.  For 
transmission  circuits  it  is  far  more  important  at  most  points  to  have  poles 


FIG.  85.— Pole  Line  from  Spier  Falls  over  Mount  McGregor. 

very  strong  rather  than  very  long.  Where  wires  or  obstructions  must 
be  crossed  by  the  high-voltage  circuits  the  poles  should  be  long  enough 
to  carry  these  circuits  well  above  everything  else.  In  the  open  country, 
where  no  obstructions  are  to  be  avoided,  it  does  not  pay  to  use  poles  with 
a  length  greater  than  thirty-five  feet. 

Short  poles  offer  less  surface  to  the  wind,  the  length  of  the  lever 
through  which  wind  pressure  acts  to  break  the  pole  at  the  ground  de- 
creases with  the  length  of  pole,  and  the  shorter  the  poles  the  smaller  is 
the  strain  on  struts  and  guy  wires.  If  poles  are  only  thirty  or  thirty-five 


254     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


feet  long,  they  may  be  large  in  diameter  without  excessive  cost.  As  a 
rule,  no  pole  should  be  used  with  a  top  less  than  seven  inches  in  diame- 
ter, and  a  pole  with  thi  stop  should  not  be  required  to  carry  more  than 
three  wires.  A  pole  with  seven-  or  eight-inch  top  and  thirty  feet  long 
should  measure  not  less  than  twelve  inches  in  diameter  at  the  butt.  For 
longer  poles  the  diameters  at  the  butt  should  increase  up  to  at  least  eigh- 
teen inches  for  a  round  pole  sixty  feet  long. 

In  the  New  Hampshire  transmission  above  named  the  standard 
length  of  poles  is  thirty-five  feet.  On  the  line  between  Canon  Ferry  and 
Butte  the  poles  range  from  thirty-five  to  ninety  feet  in  length.  The 
round  cedar  poles  used  in  the  Colgate  and  Oakland  line  range  from 
twenty-five  to  sixty  feet  in  length,  from  eight  to  twelve  inches  diameter 
at  the  top,  and  from  twelve  to  eighteen  inches  diameter  at  the  butt.  On 
the  line  between  Electra  and  San  Francisco  the  square-sawed  redwood 
poles  are  reported  to  have  the  following  dimensions,  in  a  paper  read  at 
the  annual  convention  of  Edison  Illuminating  Companies  in  1902. 


Height, 
Felt. 

Top, 
Inches. 

Butt, 
Inches. 

Depth 
in  Ground. 

35 

7X    7 

12      X    12 

5-5 

40 

8X    8 

13*  X  13^ 

6 

45 

9X    9 

15   x  15 

6-5 

£ 

10  X  10 
ii  X  ii 

16    X  16 
17    X  17 

8 

The  relative  dimensions  of  these  poles  are  of  interest  because,  being 
sawed  from  the  trunks  of  large  trees,  they  could  have  any  desired  meas- 
urements at  the  tops  and  butts.  These  poles,  over  the  greater  part 
of  the  line,  carried  the  three  aluminum  cables  of  471,034  circular  mils 
each,  previously  mentioned.  Depth  to  which  poles  are  set  in  the  ground 
ranges  from  about  five  feet  for  twenty-five-  or  thirty-foot  poles  to  eight 
feet  for  poles  sixty  feet  long.  In  locations  where  the  soil  is  very  soft  or 
where  poles  must  resist  heavy  strains  the  stability  of  each  pole  may  be 
much  increased  by  digging  the  hole  two  feet  or  more  larger  in  diameter 
than  the  butt  of  the  pole,  and  'then  filling  in  cement  concrete — one 
part,  by  measure,  of  Portland  cement,  three  of  sand  and  five  of  broken 
stone — all  around  the  butt  of  the  pole  after  it  is  in  the  hole.  The  butts 
of  poles  up  to  a  point  one  foot  or  more  above  the  ground  line  are  fre- 
quently treated  with  hot  tar,  pitch,  asphalt,  or  carbolineum  before  the 
poles  are  erected,  and  in  Salt  Lake  City  salt  is  said  to  be  used  around  pole 
butts  after  they  are  in  the  hole. 


POLE  LINES  FOR  POWER  TRANSMISSION. 


255 


In  some  cases  the  poles  of  transmission  lines  are  painted  over  their 
entire  length.  Pole  tops  should  always  be  pointed  or  wedge-shaped,  to 
shed  water,  and  paint  or  tar  should  be  applied  to  these  tops.  In  some 
cases  poles  are  filled  with  crude  petroleum  or  other  preservative  com- 
pound in  iron  retorts,  where  moisture  is  withdrawn  from  the  pole  by 
exhausting  the  air,  and  then,  after  treatment  with  dry  steam,  the  poles 
have  the  compound  forced  into  them  by  hydraulic  pressure. 

In  favorable  soils  cedar  poles  may  remain  fairly  sound  for  twenty 
years,  chestnut  poles  more  than  one-half  of  that  time,  and  spruce  and 
,pine  about  five  years.  Poles  up  to  forty  feet  in  length  may  be  readily 


FIG.  86.— Chambly-Montreal  Line 


the  Richelieu  River. 


set  with  pike  poles,  but  when  they  are  much  longer  than  this  a  derrick 
will  save  time  and  labor.  A  derrick  should  have  a  little  more  than  one- 
half  the  length  of  the  poles  to  be  set. 

Poles  should  be  guyed  or  braced  at  all  points  where  there  are  material 
changes  in  the  direction  of  the  line,  and  on  long  straight  stretches  about 
every  fifth  pole  should  be  guyed  or  braced  in  both  directions  to  prevent 
the  poles  setting  back  when  the  line  wire  is  cut  or  broken  at  any  point. 
Where  there  is  room  for  wooden  struts,  as  on  a  private  right  of  way,  they 
should  be  used  instead  of  guys  because  of  their  more  substantial  character 
and  the  higher  security  of  insulation  thus  obtained.  Ordinary  strain 
insulators  cannot  be  relied  on  with  lines  that  operate  at  very  high 
voltages,  and  where  guys  must  be  used  a  timber  four  by  six  inches  and 


256    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


ten  to  twenty  feet  long  may  have  the  guy  twisted  about  each  end  of 
it  and  be  used  as  a  strain  insulator.  A  guy  or  strut  should  come  well  up 
under  the  lower  cross-arm  on  a  pole  to  avoid  breaking  of  the  pole  at  the 
point  of  attachment. 

Where  poles  have  heavy  circuits  and  several  cross-arms  each  it  is 


sometimes  desirable  to  attach  a  guy  or  strut  beneath  the  lowest  arm  and 
also  a  guy  close  to  the  pole  top.  Galvanized  iron  or  steel  wire  is  the 
material  best  suited  for  guys,  and  the  cable  form  has  greater  strength 
and  is  more  flexible  than  solid  wire. 

On  the  transmission  line  between  Electra  and  San  Francisco,  which 
is  intended  to  operate  at  60,000  volts,  the  use  of  guys  has  been  mostly 
avoided  and  struts  employed  instead.  Where  a  guy  had  to  be  used,  a 


POLE  LINES  FOR  POWER  TRANSMISSION.          257 

strain  insulator  of  wood  six  by  six  inches  and  twenty  feet  long  was  in- 
serted in  it. 

The  number  and  spacing  of  cross-arms  on  the  poles  of  transmission 
lines  are  regulated  by  the  number  of  circuits  that  each  pole  must  carry 
and  by  the  desired  distance  apart  of  the  wires.  Formerly  it  was  com- 
mon to  carry  two  or  more  circuits  on  a  single  line  of  poles,  but  now 
a  frequent  practice  is  to  give  each  pole  line  only  one  circuit  and  each 
pole  only  one  cross-arm,  except  that  a  small  cross-arm  for  a  telephone 
circuit  is  placed  some  feet  below  the  power  wires.  With  only  one^ 
transmission  circuit  per  pole  line,  one  wire  is  usually  placed  at  the 
top  of  the  pole  and  the  other  two  wires  at  opposite  ends  of  the  single 
cross-arm.  The  older  pole  line  for  the  transmission  between  Niagara 
Falls  and  Buffalo  carried  two  cross-arms  per  pole  for  the  power  wires, 
these  cross-arms  being  two  feet  apart.  Each  cross-arm  was  of  yellow 
pine,  twelve  feet  long,  four  by  six  inches  in  section,  and  intended  to 
carry  four  three-wire  circuits,  but  only  two  circuits  have  been  erected 
on  these  two  cross-arms.  On  the  later  pole  line  for  this  same  transmis- 
sion each  pole  carries  two  cross-arms,  the  upper  intended  for  four  and 
the  lower  cross-arm  for  two  wires,  so  that  one  three-wire  circuit  may  be 
strung  on  each  side  of  the  poles,  two  wires  on  the  upper  and  one  on  the 
lower  arm  in  the  form  of  an  equilateral  triangle.  The  pole  lines  between 
Canon  Ferry  and  Butte,  Colgate  and  Oakland,  and  Electra  and  San 
Francisco  all  have  only  one  cross-arm  for  power  wires  per  pole,  and  the 
third  wire  of  the  circuit  in  each  case  is  mounted  at  the  top  of  the  pole 
so  that  the  three  conductors  are  at  the  corners  of  an  equilateral  triangle. 

This  relative  position  of  the  conductors  makes  it  easy  to  transpose 
them  as  often  as  desired.  On  the  line  from  Canon  Ferry  to  Butte  the 
cross-arms  are  each  eight  feet  long  with  two  holes  for  pins  seventy-eight 
inches  apart,  and  are  attached  to  the  pole  five  feet  ten  and  one-half 
inches  from  the  top.  Gains  for  cross-arms  should  be  cut  from  one  to 
two  inches  deep  in  poles  before  they  are  raised,  and  one  hole  for  three- 
quarters  or  seven-eighths-inch  bolt  should  be  bored  through  the  centre  of 
the  cross-arm  and  of  the  pole  at  the  gain.  Each  cross-arm  should  be 
attached  to  the  pole  by  a  single  bolt  passing  entirely  through  the  pole 
and  cross-arm  with  a  washer  about  three  inches  in  diameter  next  to  the 
cross-arm.  One  large  through  bolt  weakens  the  pole  and  arm  less  than 
two  smaller  bolts  or  lag-screws,  and  the  arm  can  be  more  easily  replaced 
if  there  is  only  one  bolt  to  remove.  Alternate  poles  in  a  line  should 
have  their  cross-arms  bolted  on  opposite  sides,  and  at  corners  double 
arms  should  be  used. 


258    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

Yellow  pine  is  a  favorite  wood  for  cross-arms,  though  other  varieties 
are  also  used.  The  large,  long  pins  necessary  on  high  voltage  lines  tend 
to  increase  the  sectional  area  of  cross-arms,  and  a  section  less  than  five 
and  one-half  by  four  and  one-half  inches  is  seldom  desirable.  On  the 
line  between  Electra  and  San  Francisco,  which  carries  the  three  alu- 
minum cables  of  471,034  circular  mils  each,  the  cross-arms  of  Oregon 
pine  have  a  section  of  six  by  six  inches  each.  Standard  dimensions  of 
some  smaller  cross-arms  are  four  and  three-quarters  by  three  and 
three-quarters  inches,  but  it  may  be  doubted  whether  these  arms  are 


FIG.  88.— Tail  Race  and  Pole  Line  at  Chambly,  Quebec  Power-station, 

strong  enough  for  long  transmission  work.  Cross-arms  should  be 
surfaced  all  over  and  crowned  one-quarter  to  one-half  inch  on  top  so 
as  to  shed  water.  After  being  kiln  dried,  cross-arms  should  be  boiled 
in  asphaltum  or  linseed  oil  to  preserve  the  wood  and  give  it  higher 
insulating  properties.  Cross-arms  longer  than  five  feet  should  be 
secured  by  braces  starting  at  the  pole  some  distance  below  each  arm 
and  extending  to  points  on  the  arm  about  half-way  between  the  pole 
and  each  end  of  the  arm. 

Each  brace  may  be  of  flat  bar  iron  about  one  and  one-half  by  one- 
quarter  inch  in  section,  or  the  brace  for  both  ends  of  an  arm  may  be  made 


POLE  LINES  FOR  POWER  TRANSMISSION.         259 

of  a  single  piece  of  angle-iron  bent  into  the  proper  shape.  For  high- 
voltage  lines  it  is  undesirable  to  employ  iron  braces  of  any  sort,  since  these 
braces  form  a  path  of  low  resistance  that  comes  much  too  close  to  the 
pins  on  which  the  insulators  and  wires  are  mounted.  Braces  formed  of 
hard  wood  are  much  better  as  to  insulation,  and  such  braces  of  maple 
are  in  use  on  the  line  between  Butte  and  Canon  Ferry  where  the  voltage 
is  50,000.  Each  brace  on  that  line  is  thirty-six  inches  long  and  three 
inches  wide,  with  one  end  bolted  to  the  centre  of  its  pole  and  the  other 
end  to  the  cross-arm  twenty-three  inches  from  the  pole  centre. 

The  line  from  Electra  has  hard-wood  braces  secured  with  wood  pins. 

Wood  is  the  most  common  material  for  pins  on  which  to  mount  the 
insulators  of  high-voltage  transmission  circuits.  Iron  has  been  used  for 
pins  to  some  extent,  and  its  use  is  on  the  increase.  Oak  and  locust  pins 
are  generally  used,  the  latter  being  stronger  and  more  lasting.  In  Cali- 
fornia, pins  of  eucalyptus  wood  are  much  used  and  are  said  to  be  stronger 
than  locust.  All  wooden  pins  should  be  boiled  several  hours  in  linseed 
oil  after  being  well  dried.  This  increases  the  insulating  and  lasting 
properties  of  the  pins. 

High-voltage  lines  require  long  pins  to  hold  the  lower  edges  of  in- 
sulators well  above  the  cross-arms,  and  these  pins  must  be  much  stronger 
than  those  used  on  ordinary  lines,  because  of  the  increased  leverage  of 
each  wire. 

A  pin  twelve  inches  long  over  all  and  having  a  diameter  of  one  and 
one-half  inches  in  the  part  that  enters  the  cross-arm  has  been  much 
used  for  transmission  circuits,  but  is  much  too  short  and  weak  for 
high  voltages.  On  the  5o,ooo-volt  line  between  Canon  Ferry  and  Butte 
the  pins  are  seasoned  oak  boiled  in  paraffin.  Each  of  these  pins  is 
seventeen  and  one-half  inches  long,  two  and  one-half  inches  in  diameter 
for  a  length  of  four  and  one-half  inches  in  the  middle  part,  two  inches  in 
diameter  for  a  length  of  five  and  one-half  inches  that  fits  into  the  cross- 
arm  or  pole  top,  and  one  and  one-half  inches  in  diameter  at  the  top  of  the 
thread  inside  of  the  insulator.  These  pins  hold  the  outside  edges  of  the 
insulators  nine  inches  above  the  tops  of  cross-arms.  Each  of  these  pins 
is  held  in  its  socket  by  a  three-eighths-inch  bolt  that  passes  entirely  through 
the  pin  and  the  cross-arm  or  pole  top. 

On  the  line  between  Electra  and  San  Francisco  the  pins  are  each 
sixteen  and  seven-eighths  inches  long,  two  and  three-quarters  inches  in 
diameter  at  the  largest  central  part,  and  two  and  one-quarter  inches  in 
diameter  in  the  lower  part,  five  inches  long,  that  fits  into  the  cross-arm 
or  pole  top.  One  of  these'pins  broke  at  the  shoulder  with  a  pull  of  2,200 


26o     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

pounds  at  the  threaded  part.  Carriage  bolts  one-half  inch  in  diameter 
pass  through  the  cross-arm  and  pin  two  inches  from  the  top  of  the  arm, 
and  one  bolt  three  inches  from  the  pin  on  each  side.  Without  these 
bolts  the  arms  split  on  test  with  a  pull  of  1,200  pounds  on  the  pin,  but 
with  the  bolts  the  pin  broke  as  above. 


CHAPTER  XIX. 

ENTRIES  FOR  ELECTRIC  TRANSMISSION  LINES. 

THE  entrance  of  transmission  lines  into  generating  plants  and  sub- 
stations presents  special  problems  in  construction  and  insulation.  One 
of  these  problems  has  to  do  with  the  mechanical  security  of  each  conductor 
at  the  point  where  it  passes  through  the  side  or  roof  of  the  station.  Con- 
ductors are  sometimes  attached  to  the  station  so  that  the  strain  of  the 
line  is  borne  by  the  side  wall  where  they  enter  and  tends  to  pull  it  out 
of  line. 

This  practice  has  but  little  to  commend  it,  aside  from  convenience, 
for  unless  the  conductors  are  rather  small,  or  the  wall  of  the  station  is 
unusually  heavy,  the  pull  of  the  former  is  apt  to  bulge  the  latter  in  the 
course  of  time.  For  any  heavy  line  the  end  strain  is  ultimately  most 
suitably  taken  by  an  anchor  securely  fixed.  As  special  insulators  must 
be  used  where  a  conductor  is  secured  directly  to  such  an  anchor,  it  is 
usually  more  convenient  to  set  one  or  more  heavy  poles  with  double  cross- 
arms  at  the  end  of  a  line,  and  then  to  make  these  poles  secure  by  large 
struts,  or  by  guys  attached  to  anchors.  Extra  heavy  cross-arms  on  these 
end  poles  should  be  provided  with  iron  pins  for  the  line  insulators ;  two 
or  more  of  the  insulators  mounted  in  this  way  within  a  few  feet  of  each 
other,  for  each  wire,  will  stand  up  against  the  end  strain  on  almost  any 
line. 

Insulators  that  are  to  take  the  end  strain  of  a  line  in  this  way  should 
allow  attachment  of  the  wire  at  the  side,  so  that  the  force  exerted  by  each 
conductor  tends  to  press  the  insulator  against  the  side  of  its  pin,  rather 
than  to  pull  off  the  top  of  the  insulator.  The  end  strain  of  the  line  hav- 
ing been  taken  on  poles  close  to  the  station,  the  conductors  may  be  at- 
tached to  insulators  on  the  wall,  the  latter  thus  being  subjected  to  very 
little  mechanical  strain. 

Overhead  lines  usually  enter  a  station  through  one  of  its  side  walls, 
but  an  entry  may  be  made  in  the  roof.  It  is  desirable  to  have  a  side  entry 
on  the  gable  end  of  a  building  rather  than  on  a  side  below  the  eaves 
where  there  will  be  much  dripping  of  water.  If  an  entry  must  be  made 
below  the  eaves,  a  shelter  should  be  provided  above  the  entry,  and  the 

261 


262     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

roof  of  this  shelter  should  have  a  gutter  that  will  carry  water  away  from 
the  wires. 

Entrance  of  each  conductor  into  a  station  must  be  effected  in  such  a 
way  that  ample  insulation  of  the  circuit  will- be  maintained,  and  in  some 
cases  so  that  rain,  snow,  and  wind  will  be  excluded.  The  line  voltage 
and  the  climate  where  the  station  is  located  thus  have  an  important 
bearing  on  the  form  of  entry  that  is  suitable  in  any  particular  case. 

The  simplest  form  of  entry  for  a  high-voltage  line  is  a  clear  opening, 
usually  circular  in  form,  through  the  wall  of  the  station  for  each  wire. 
Insulators  for  each  wire  should  be  provided  both  inside  and  outside  of 
the  wall  to  hold  the  wire  at  the  centre  of  this  opening.  Such  insulators 
are  usually  most  conveniently  supported  by  fixtures  attached  to  both  sides 
of  the  wall,  and  insulators  on  the  outside  should  of  course  be  kept  in  an 
upright  position,  unless  completely  protected  from  rain  and  snow. 

The  diameter  of  the  openings  through  the  wall  should  be  great 
enough  to  prevent  any  visible  discharge  of  current  between  the  wire  and 
wall  under  the  worst  conditions  of  snow,  rain,  fog,  or  dust.  Such  an 
opening  must,  therefore,  increase  in  diameter  with  the  voltage  of  the  line. 
The  larger  these  openings  for  the  line  wires,  the  greater  is  the  opportunity 
for  rain,  snow,  dust,  and  cold  air  to  enter  the  station  through  them. 

Openings  may  be  so  protected  as  to  keep  out  snow  and  rain  by  means 
of  shelters  on  the  outside  of  the  wall  on  which  they  are  placed,  but  such 
shelters  cannot  keep  out  the  cold  air.  If  the  openings  for  the  entrance 
of  wires  are  located  in  the  wall  of  a  room  that  contains  air-blast  trans- 
formers, the  area  of  openings  for  circuits  of  very  high  voltage  may  be 
no  greater  than  is  necessary  to  allow  the  escape  of  heated  air  from  the 
transformers. 

The  milder  the  climate,  other  factors  being  the  same,  the  higher  the 
voltage  of  circuits  which  may  enter  a  station  through  openings  that  are 
free  for  the  movement  of  air.  With  circuits  of  only  moderate  voltage, 
say  less  than  15,000,  it  is  quite  practicable  to  admit  wires  to  a  station 
through  perfectly  free  openings,  in  the  coldest  parts  of  the  United  States. 
With  voltages  of  20,000  to  60,000  it  is  often  necessary,  in  the  colder  parts 
of  the  country,  to  close  the  opening  in  the  wall  through  which  each  wire 
enters  with  a  disc  of  insulating  material. 

In  order  to  keep  the  current  leakage  over  these  discs  within  proper 
limits,  the  diameters  of  the  discs  must  increase  with  the  voltage  of  the 
circuit.  This  increase  of  disc  diameter  obviously  lengthens  the  path  of 
leakage  current  over  the  disc  surface.  Where  the  openings  in  a  wall  for 
the  entrance  of  high-voltage  circuits  are  closed  by  insulating  discs  about 


ENTRIES  FOR  TRANSMISSION  LINES.  263 

the  wires,  these  discs  may  make  actual  contact  with  bare  wires,  or  the 
wire  at  each  entry  may  have  some  special  insulation. 

In  the  side  wall  of  the  sub-station  at  Manchester,  N.  H.,  the  entrance 
of  transmission  lines  from  four  water-power  plants  is  provided  for  by 
circular  openings  in  slate  slabs  that  are  built  into  the  brickwork.  The 
transmission  circuits  from  three  of  the  water-power  plants  operate  at 
10,000  to  12,000  volts,  and  the  circuit  from  the  fourth  plant  at  about 
6,000  volts.  Circular  openings  in  the  slate  slabs  are  each  five  inches  in 
diameter,  and  they  are  spaced  twelve  to  fifteen  inches  between  centres. 
A  single  wire  enters  through  each  of  these  openings  and  is  held  at  the 
centre  by  insulators  both  inside  and  outside  of  the  wall.  Each  wire  is 
bare  where  it  passes  through  the  slate  slab,  and  the  circular  openings  are 
not  closed  in  any  way.  The  largest  wires  passing  through  these  five- 
inch  circular  openings  in  the  slate  slabs  are  of  solid  copper,  No.  o,  of 
0.3 2 5-inch  diameter  each. 

Before  passing  through  the  opening  in  the  slate  slabs  the  wires  of 
these  transmission  circuits  are  tied  to  regular  line  insulators  supported 
by  cross-arms  secured  to  the  outside  of  the  brick  wall  by  iron  brackets. 
The  point  of  attachment  of  each  wire  to  its  insulator  is  about  nine  inches 
below  the  centre  of  the  circular  hole  by  which  it  enters  the  sub-station. 

This  Manchester  sub-station  is  equipped  with  air-blast  transformers 
from  which  the  hot  air  is  discharged  into  the  same  room  that  the  trans- 
mission lines  enter.  Along  one  side  of  the  sub-station  there  are  twenty- 
seven  of  these  five-inch  circular  openings  in  the  slate  slabs  for  entrance 
of  the  high- voltage  lines,  and  on  another  side  of  the  sub-station  there  are 
a  greater  number  of  smaller  openings  for  the  distribution  circuits.  Were 
it  not  for  the  air-blast  transformers,  all  of  these  openings  would  probably 
admit  more  air  than  would  be  desirable  in  a  climate  as  cold  as  that  at 
Manchester. 

Another  example  of  openings  in  the  walls  of  a  station  for  the  entrance 
of  transmission  circuits,  where  there  is  free  movement  of  the  air  between 
the  inside  and  outside  of  the  building,  is  that  of  the  33,ooo-volt  line  be- 
tween Santa  Ana  River  and  Los  Angeles,  Cal.  In  this  case  a  sewer  pipe 
twelve  inches  in  diameter  is  built  into  the  wall  of  the  station  for  each 
wire  of  the  line,  so  that  there  is  a  free  opening  of  this  size  from  inside  to 
outside. 

Each  wire  of  the  33,000- volt  circuit  enters  the  station  through  the 
centre  of  one  of  these  twelve-inch  pipes,  and  is  thus  surrounded  by  six 
inches  of  air  on  every  side.  As  the  temperature  near  Los  Angeles  sel- 
dom or  never  goes  down  to  zero,  these  large  openings  do  not  admit 


264     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

enough  air  to  be  objectionable.  Besides  this  mild  climate,  air-blast 
transformers  add  to  the  favorable  features  in  the  stations  having  the 
twelve-inch  openings. 

In  another  case,  however,  where  the  openings  for  the  entrance  of 
wires  of  very  high  voltage  allow  free  movement  of  air  between  the  inside 
and  outside  of  the  station,  the  climate  is  cold  and  the  winter  temperatures 
go  down  to  30°  or  more  below  zero.  This  condition  exists  on  the  25,000- 
volt  line  between  Apple  River  Falls  and  St.  Paul,  where  six  No.  2  wires 
enter  the  generating  station  through  plain  circular  openings  in  the  brick 
side  wall  of  a  small  extension  where  the  lightning  arresters  are  located. 
Air-blast  transformers  are  located  in  the  end  of  the  station  next  to  this 
lightning-arrester  house,  but  it  is  not  certain  that  the  hot  air  from  them 
escapes  through  the  openings  for  the  wires. 

In  another  case  where  the  climate  is  about  as  cold  as  that  just  named, 
a  gallery  is  built  along  one  side  of  the  exterior  of  the  station  at  some  dis- 
tance above  the  ground,  and  two  openings  are  provided  for  each  wire  of 
the  high-tension  line.  One  of  these  two  openings  is  in  the  horizontal 
floor  of  the  gallery  and  allows  the  entrance  of  the  wire  from  the  outside, 
and  the  other  opening  is  in  the  side  wall  of  the  station  against  which  the 
gallery  is  built.  The  two  openings  for  each  wire  being  thus  at  right 
angles  to  each  other,  and  the  opening  to  the  outside  air  being  protected 
from  the  wind  by  its  horizontal  position,  no  more  than  a  permissible 
amount  of  cold  air,  it  is  said,  finds  its  way  into  the  station. 

In  some  cases  with  lines  of  moderate  voltage,  say  10,000  to  15,000, 
and  in  probably  the  majority  of  cases  with  lines  of  25,000  volts  or  more, 
the  entry  for  the  high-tension  wires  is  entirely  closed.  An  example  of 
this  practice  may  be  seen  at  the  various  sub-stations  of  the  New  Hamp- 
shire Traction  Company,  which  are  located  along  their  12,000- volt  line 
between  Portsmouth  and  Pelham,  in  that  State. 

For  the  entry  of  each  wire  on  these  lines  a  sixteen-inch  square  open- 
ing is  made  in  the  brick  wall  of  the  sub-station.  On  the  outside  of  this 
wall  a  box  is  built  about  a  group  of  three  or  more  of  these  openings 
located  side  by  side.  The  top  or  roof  of  this  box  is  formed  by  a  slab  of 
bluestone  three  inches  thick,  which  is  set  into  the  wall  and  extends 
twenty-six  inches  from  the  face  of  the  wall,  with  a  slight  slope  from  the 
horizontal. 

The  ends,  the  bottom,  and  the  outer  side  of  this  box  are  formed  by 
slabs  of  slate  one  inch  thick,  so  that  the  enclosed  space  has  an  area  in 
vertical  cross  section  at  right  angles  to  this  building  15.5  inches  high  and 
twenty-two  inches  wide. 


ENTRIES  FOR  TRANSMISSION  LINES.  265 


FIG.  89— Cable  Entering  Building. 


266    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

•  In  the  bottom  of  this  box  there  is  a  circular  opening  for  each  wire, 
and  into  this  opening  fits  a  heavy  glass  or  porcelain  bushing  through 
which  the  wire  passes.  After  reaching  the  inside  of  the  box  the  wire 
turns  at  right  angles  and  passes  through  the  sixteen-inch  square  opening 
into  the  sub-station.  Beneath  the  box  a  special  insulator  is  secured  by 
an  iron  bracket  to  the  outside  of  the  brick  wall  for  each  line  wire,  and  this 
insulator  takes  the  strain  of  the  wire  before  it  is  carried  up  through  the 
bushing  in  the  bottom  of  the  box.  This  form  of  entry  is  permissible 
where  the  desire  is  to  exclude  cold  air  from  the  station,  and  where  the 
voltage  is  not  high  enough  to  cause  serious  leakage  over  the  surface  of 
the  bushing  and  the  slate  forming  the  bottom  of  the  box.  In  all  of  the 
cases  above  mentioned  the  wires  used  to  enter  the  stations  were  the  regu- 
lar line  conductors  and  were  bare. 

Another  type  of  entry  in  sub-stations  is  that  employed  on  the  extensive 
transmission  system  between  Spier  Falls,  Schenectady,  and  Albany, 
N.  Y.  The  maximum  voltage  on  this  system  is  30,000,  and  the  lines 
usually  enter  each  sub-station  through  the  brick  wall  at  one  of  its  gable 
ends.  Outside  of  and  about  the  entry  of  each  circuit  or  group  of  circuits  a 
wooden  shelter  is  built  on  the  brick  wall  of  the  sub-station.  Each  shelter 
has  a  slanting  roof  that  starts  from  the  brick  wall  at  some  distance  above 
the  openings  for  the  entrance  of  the  line,  and  terminates  in  a  gutter.  The 
front  of  each  shelter  is  carried  dov/n  three  feet  below  the  centre  of  the 
openings  in  the  brick  wall,  and  the  ends  go  still  lower.  The  front  of 
each  shelter  is  four  feet  in  height,  is  four  feet  from  the  face  of  the  brick 
wall,  and  has  a  circular  opening  of  lo-inch  diameter  for  each  wire  of 
the  transmission  line. 

In  line  with  each  circular  opening  in  the  wooden  shield  there  is  an 
opening  of  1 5-inch  diameter  in  the  brick  wall  of  the  sub-station,  and  into 
this  opening  in  the  brickwork  fits  a  ring  of  wood  with  1 5-inch  outside  and 
1 1  -inch  inside  diameter.  To  this  wooden  ring  a  1 5-inch  disc  of  hard  fibre 
J-inch  thick  is  secured,  and  a  porcelain  tube  24  inches  long  and  of  2-inch 
inside  diameter  passes  through  a  hole  in  the  centre  of  this  disc.  Within 
the  wooden  shield  and  in  line  with  each  circular  opening  in  it  and  with 
the  corresponding  porcelain  tube  through  the  fibre  disc  a  line  insulator 
is  secured.  Within  the  sub-station  and  in  line  with  each  tube  there  is 
also  an  insulator,  and  the  two  insulators  near  opposite  ends  of  each  tube 
hold  the  line  wire  that  passes  through  it  in  position. 

Each  wire  of  the  transmission  lines,  of  which  the  largest  is  No.  ooo 
solid  of  o.4io-inch  diameter,  terminates  at  one  of  the  insulators  within 
the  wooden  shield,  and  is  there  connected  to  a  special  insulated  wire  that 


ENTRIES  FOR  TRANSMISSION  LINES.  267 

passes  through  one  of  the  porcelain  tubes  into  the  sub-station.  A  copper 
trolley  sleeve  1 2  inches  long  is  used  to  make  the  soldered  connection  be- 
tween the  bare  line  wire  and  the  insulated  conductor  that  passes  through 
the  porcelain  tube.  Each  of  these  entry  cables,  whatever  its  size,  is 
insulated  first  with  a  layer  of  rubber  -sVmch  thick,  then  with  varnished 
cambric  wound  on  to  a  thickness  of  sV-inch,  and  lastly  with  two  layers 
of  weather-proof  braid  outside  of  the  cambric.  This  form  of  closed 
entry  for  the  transmission  lines  obviously  excludes  snow,  rain,  cold  air, 
and  dust  from  the  station.  Whether  the  fibre  discs  and  wooden  rings, 
together  with  the  insulation  on  the  entry  cables,  are  as  desirable  as  a 
glass  disc  at  the  entry  is  another  question. 

Another  instance  where  the  entry  for  a  high-tension  line  is  closed 
with  the  aid  of  combustible  material  is  that  of  the  2 5, coo- volt  transmission 
between  the  water-power  plant  at  Chambly,  on  the  Richelieu  River,  and 
the  sub-station  in  Montreal.  The  four  three-phase  circuits  of  this  line 
are  made  up  of  No.  oo  wires  of  o.365-inch  diameter  each,  which  enter 
the  power-station  at  Chambly  and  the  terminal-house  in  Montreal  bare, 
as  they  are  outside. 

At  each  end  of  the  line  the  wires  are  secured  to  insulators  on  a  horizon- 
tal arm  with  their  centres  twenty-two  inches  outside  of  an  end  wall  of  the 
station  or  terminal  building.  The  insulators  are  mounted  with  their 
centres  thirty  inches  apart,  and  a  few  inches  above  the  tops  of  these 
insulators  a  corresponding  row  of  wooden  bushings  pass  through  the 
wall  with  an  outward  slant. 

At  the  Chambly  end  of  the  line  each  of  these  bushings  is  of  oak, 
boiled  in  stearin,  four  inches  in  diameter  and  twelve  inches  lon|;.  At  the 
Montreal  end  the  wall  bushings  are  of  boxwood,  and  each  is  four  inches 
square  and  twelve  inches  long.  Each  of  the  wooden  bushings  carries  a 
glass  tube,  and  is  itself  held  in  position  by  the  concrete  of  the  wall  in 
which  it  is  located.  Entrance  to  the  station  by  each  of  the  bare  No.  oo 
wires  is  gained  through  one  of  these  glass  tubes,  and  cold  air  is  ex- 
cluded. 

Quite  a  different  type  of  closed  entry  for  the  wires  of  a  transmission 
line  is  in  use  on  that  between  Shawinigan  Falls  and  Montreal,  which 
operates  at  50,000  volts.  For  the  entry  of  each  of  the  three  aluminum 
cables  that  make  up  this  line,  each  cable  being  composed  of  seven  No.  6 
B.  &  S.  gauge  wires,  a  tile  pipe  of  twenty-four-inches  diameter  was  set 
into  the  station  wall.  The  end  of  each  tile  pipe  is  closed  by  a  glass  plate, 
with  a  small  hole  at  its  centre,  through  which  the  cable  passes. 

As  the  cable  is  thus  held  twelve  inches  from  the  terra  cotta  pipe  all 


268     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  way  around,  any  leakage  of  current  must  pass  over  this  length  of  glass 
surface  at  each  cable  or  through  the  air. 

A  heavy  coating  of  frost  sometimes  collects  on  these  plates,  and  this 
increases  the  amount  of  current  leakage  over  them.  Surface  leakage  in 
a  case  of  this  sort,  of  course,  varies  with  the  size  of  the  glass  plate,  and 
if  a  tile  pipe  is  used  the  limit  of  size  is  soon  reached. 

There  seems  to  be  no  good  reason,  however,  why  a  glass  plate  of  any 
desired  dimensions  should  not  be  set  directly  into  the  brick  wall  of  a 
station  for  each  line  wire  and  the  tile  pipes  entirely  omitted.  This  plan 
is  followed  on  the  system  of  the  Utah  Light  &  Power  Company,  which 
extends  to  Salt  Lake  City,  Ogden,  Provo,  and  a  number  of  other  points 
in  that  State. 

On  the  40,ooo-volt  line  of  that  system  an  entry  for  each  wire  is  pro- 
vided by  setting  two  plates  of  glass  into  the  brick  wall,  one  plate  being 
flush  with  the  inner  surface  and  the  other  with  the  outer  surface  of  the 
wall. 

In  the  centre  of  each  plate  there  is  a  hole  of  about  2. 5 -inch  diameter, 
into  which  a  glass  or  porcelain  tube  fits.  The  line  wire  enters  the  station 
through  this  tube,  and  it  does  not  appear  that  any  shelter  for  the  glass 
plates  is  located  outside  of  the  building.  An  entry  of  this  type  for  the 
40,ooo-volt  line  with  glass  plates  in  a  brick  wall  at  a  gable  end  of  the 
Murphy  mill  is  said  to  have  given  satisfactory  results  during  four  years, 
though  that  wall  faces  the  southwest,  from  which  direction  most  of  the 
storms  come.  At  this  entry  each  glass  plate  is  not  more  than  eighteen 
inches  in  diameter,  and  the  wires  are  about  four  feet  apart.  On  a 
1 6,000- volf  line  of  the  same  company,  a  glass  plate  twelve  inches  square 
with  a  three-quarter-inch  hole  at  its  centre,  and  the  bare  wire  passing 
through  without  a  tube,  has  given  results  that  were  entirely  satisfactory. 

Two  quite  different  types  of  entry  to  stations  are  used  on  the  50,000- 
volt  line  between  Canon  Ferry  and  Butte,  Mont.  One  type,  employed 
at  the  side  wall  of  a  corrugated  iron  building,  consists  of  a  thick  bushing 
of  paraffined  wood  carrying  a  glass  tube  two  inches  in  diameter,  four  feet 
long,  with  a  side  wall  of  five-eighths  to  three-quarter-inch,  through  which 
the  line  conductor  passes. 

On  the  roof  of  the  power-station  at  Canon  Ferry  a  vertical  entry  is 
made  with  the  5o,ooo-volt  circuit.  For  this  purpose  each  line  wire  is 
brought  to  a  dead  end  on  three  insulators  carried  by  a  timber  fixture  on 
the  roof.  A  vertical  tap  drops  from  each  line  wire  and  passes  through 
the  roof  and  into  the  station.  This  roof  is  of  wood,  covered  with  tin 
outside  and  lined  with  asbestos  inside.  Each  tap  is  an  insulated  wire, 


ENTRIES  FOR  TRANSMISSION  LINES.  269 

and  elaborate  methods  are  adopted  in  the  way  of  further  insulation,  and 
to  prevent  water  from  following  the  wire  down  through  the  roof. 

Over  the  point  of  entrance  sits  a  large  block  of  paraffined  wood  with 
a  central  hole,  and  down  through  this  hole  passes  a  long  cylinder  of  paper 
that  extends  some  distance  above  the  block.  Into  the  top  end  of  this 
cylinder  fits  a  wood  bushing,  and  a  length  of  the  tap  wire  that  has  been 
served  with  a  thick  layer  of  rubber  is  tightly  enclosed  by  this  bushing. 
The  rubber-covered  portion  of  the  tap  wire  also  extends  above  the  bush- 
ing, and  has  taped  to  it  a  paper  cone  that  comes  down  over  the  top  of  the 
paper  cylinder  to  keep  out  the  water.  On  the  outside  of  this  paper 
cylinder,  at  a  lower  point,  a  still  larger  paper  cone  is  attached  to  prevent 
water  from  following  the  cylinder  down  through  the  wooden  block.  At 
the  lower  end  of  the  paper  cylinder,  within  the  station,  there  is  another 
bushing  of  wood,  and  between  this  and  the  wooden  bushing  at  the  top 
of  the  cylinder  and  inside  of  the  paper  cylinder  there  is  a  long  glass  tube. 
Down  through  this  tube  and  into  the  station  the  insulated  tap  wire 
passes. 

From  the  experience  thus  far  gained  with  high-voltage  lines,  it  seems 
that  their  entrance  into  stations  should  always  be  at  a  side  wall,  unless 
there  is  some  imperative  reason  for  coming  down  through  the  roof.  If 
climatic  conditions  permit,  no  form  of  entry  can  be  more  reliable  than  a 
plain,  ample  opening  through  the  wall  with  a  large  air-space  about  each 
wire.  If  the  opening  must  be  closed,  it  had  better  be  done  with  one  or 
more  large  plates  of  thick  glass  set  directly  into  the  brickwork  of  the  wall. 
Some  additional  insulation  is  obtained  by  placing  a  long  glass  or  porcelain 
tube  over  each  wire  where  it  passes  through  the  central  hole  in  the  glass 
plates.  Each  conductor  should  be  bare  at  the  entry,  as  it  is  on  the  line. 
Some  of  the  above  examples  of  existing  practice  in  entries  for  transmis- 
sion lines  are  taken  from  Vol.  xxii.,  A.  I.  E.  E. 


CHAPTER  XX. 

INSULATOR    PINS. 

WOODEN  insulator  pins  are  among  the  weakest  elements  in  electric 
transmission  systems.  As  line  voltages  have  gone  up  it  has  been  nec- 
essary to  increase  the  distances  between  the  outside  petticoats  of  insu- 
lators and  their  cross-arms  and  to  lengthen  the  insulators  themselves  in 
order  to  keep  the  leakage  of  current  between  the  conductors  within  per- 
missible limits.  To  reduce  the  leakage,  the  wires  on  most  lines  are 
located  at  the  tops  instead  of  in  the  old  position  at  the  sides  of  their 
insulators. 

All  this  has  tended  to  a  large  increase  of  the  mechanical  strains  that 
operate  to  break  insulator  pins  at  the  point  where  they  enter  the  cross- 
arm,  because  the  strain  on  each  line  wire  acts  with  a  longer  leverage. 
Again,  it  is  sometimes  necessary  that  transmission  lines  make  long  spans 
across  rivers  or  elsewhere,  and  a  very  unusual  strain  may  be  put  on  the 
insulator  pins  at  these  places. 

As  long  as  each  electric  system  was  confined  to  a  single  city  or  town 
a  broken  insulator  pin  could  be  quickly  replaced,  and  any  material  inter- 
ruption of  service  from  such  a  cause  was  improbable.  Where  the  light 
and  power  supply  of  a  city,  however,  depends  on  a  long  transmission  line, 
as  is  now  the  case  in  many  instances,  and  where  the  line  voltage  is  so  great 
that  contact  between  a  wire  and  a  cross-arm  will  result  in  the  speedy 
destruction  of  the  latter  by  burning,  a  broken  pin  may  easily  lead  to  a 
serious  interruption  of  the  service. 

Besides  the  increase  of  mechanical  strains  on  insulator  pins,  there  is 
the  danger  of  destruction  of  wooden  pins  by  charring,  burning,  and  other 
forms  of  disintegration  due  to  leakage  of  current  over  the  insulators. 
This  danger  was  entirely  absent  in  the  great  majority  of  cases  so  long  as 
lines  were  local  and  operated  at  only  moderate  voltages.  These  several 
factors  combined  are  bringing  about  marked  changes  in  design. 

On  straight  portions  of  a  transmission  line  the  insulator  pins  are  sub- 
ject to  strains  of  two  principal  kinds.  One  of  these  is  due  directly  to  the 
weight  of  the  insulators  and  line  wire,  and  acts  vertically  to  crush  the  pins 
by  forcing  them  down  onto  the  cross-arm.  The  other  is  due  to  the  hori- 

270 


INSULATOR  PINS.  271 

zontal  pull  of  the  line  wire,  which  is  often  much  increased  by  coatings  of 
ice  and  by  wind  pressure,  tending  to  break  the  pins  by  bending — most 
frequently  at  the  point  where  they  enter  the  cross-arm.  A  strain  of 
minor  importance  on  pins  is  that  encountered  where  a  short  pole  has  been 
set  between  two  higher  ones,  and  the  line  at  the  short  pole  tends  to  lift 
each  insulator  from  its  pin,  and  each  pin  from  the  cross-arm. 

Where  the  line  changes  its  direction,  as  on  curves  and  at  corners,  the 
side  strain  on  pins  is  greatly  increased,  and  such  places  give  by  far  the 
largest  amount  of  trouble  through  the  breaking  of  pins.  The  latter  sel- 
dom fail  by  crushing  through  the  weight  of  the  lines  they  support,  be- 
cause the  size  of  pin  necessary  to  withstand  the  bending  strain  has  a 
large  factor  of  safety  as  to  crushing  strength.  Insulators  are  sometimes 
lifted  from  wooden  pins,  and  the  threads  of  these  pins  stripped  where 
a  short  pole  is  used,  as  already  noted;  but  failure  of  this  kind  is  not 
common. 

Iron  pins  are  either  screwed  or  cemented  into  their  insulators,  but 
the  cemented  joint  is  much  more  desirable,  because  where  a  screw  joint 
is  made  the  unequal  expansion  of  the  iron  and  the  glass  or  porcelain  is 
apt  to  result  in  breakage  of  the  insulator.  Where  cement  is  used,  both 
the  pins  and  insulators  should  be  threaded  or  provided  with  shoulders 
of  some  sort,  so  that,  although  the  shoulders  of  threads  do  not  come  into 
contact  with  each  other,  they  will,  nevertheless,  help  to  secure  a  better 
hold.  Pure  Portland  cement,  mixed  with  water  to  a  thick  liquid,  has 
been  used  with  success,  the  insulator  being  placed  upside  down  and  the 
pin  held  in  a  central  position  in  the  hole  of  the  insulator  while  the  cement 
is  poured  in.  Another  cement  that  has  been  used  for  the  same  purpose 
is  a  mixture  of  litharge  and  glycerin.  Melted  sulphur  is  also  available. 

The  same  forces  that  tend  to  lift  an  insulator  from  its  pin  tend  also 
to  pull  the  pin  from  its  socket  in  the  cross-arm  or  pole  top.  With  wooden 
pins  the  time-honored  custom  has  been  to  drive  a  nail  into  the  side  of  the 
cross-arm  so  that  it  enters  the  shank  of  the  pin  in  its  socket.  This  plan 
is  good  enough  so  far  as  immediate  mechanical  strength  is  concerned,  but 
is  not  desirable,  because  it  is  hard  to  remove  a  nail  when  a  pin  is  to  be 
removed,  and  also  because  the  rust  of  the  nail  rots  the  wood.  A  better 
plan  is  to  have  a  small  hole  entirely  through  each  cross-arm  and  in- 
sulator pin  at  right  angles  to  the  shank  of  that  pin  in  its  socket,  and 
then  to  drive  a  small  wooden  pin  entirely  through  from  side  to  side. 

Some  of  the  important  factors  affecting  the  strains  on  insulator 
pins  vary  much  on  different  transmission  lines,  as  may  be  seen  from 
the  following  table  of  lines  on  which  wooden  pins  are  used.  On  the 


272     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

older  line  between  Niagara  Falls  and  Buffalo,  the  regular  length  of 
span  is  70  feet,  and  each  copper  conductor  of  350,000  circular  mils  is 
attached  to  its  insulator  7.5  inches  above  the  cross-arm.  On  the  new 


TABLE  I. — DATA  OF  LINES  ON  WOODEN  PINS. 


Location  of  the  Lines. 

Circular  Mils 
of  Each 
Conductor. 

M 
JK 

tgcng 
[i/o  .5 

Inches  from 
Wire  to 
Shank  of  Pin. 

Colgate  to  Oakland  

"|"I7?  IOO 

1  3 

Electra  to  San  Francisco 

T  C 

Canon  Ferry  to  Bulte 

tine  600 

Mu 

Mi 

Shawinigan  Falls  to  Montreal 

*l8l  7SO 

IOO 

lit 

Niagara  Falls  to  Buffalo  .  . 

+  7CQ  OOO 

7O 

»• 

Niagara  Falls  to  Buffalo  

*roO  OOO 

ry 

I  dO 

IO 

Chambly  to  Montreal  

•j-  j  ?  •?  i  QO 

QO 

si 

Colgate  to  Oakland  

*2II  6OO 

I  ^ 

*Aluminum  conductors. 


f  Copper  conductors. 


line  the  length  of  span  is  140  feet,  and  each  aluminum  conductor  of 
500,000  circular  mils  is  attached  to  its  insulator  10  inches  above  the 
cross-arm. 

TABLE  II. — DIMENSIONS  OF  WOODEN  PINS  IN  INCHES. 


Location  of  Lines. 

Length  of 
Stem. 

Length  of 
Shank. 

Diameter  of 
Shank. 

Diameter  of 
Shoulder. 

Diameter  of 
Threaded 
End. 

Length 
of  Threaded 
Part. 

Colgate  to  Oakland 

io| 

5§ 

2i 

2i 

i3 

2 

Electra  to  San  Francisco  .  .  . 

12 

41 

2* 

2! 

1  1 

2 

Caiion  Ferry  to  Butte 

I2i 

5i 

2 

Z\ 

ii 

Shawinigan  Falls  to  Montreal  
Niagara  Falls  to  Buffalo*  

fl 

1 

2f 
2 

3 

2^ 

I 

ii 

Niagara  Falls  to  Buffalo  "J"  

71 

6 

2l 

2f 

ii 

2* 

Chambly  to  IVlontrealt 

7 

c 

ii 

jl 

Canon  Ferry  to  Butte§ 

Ml 

7l 

4 

2* 

ij 

*  Pins  on  old  line, 
f  Pins  on  new  line. 


t  Approximate  dimensions. 
§  Pole  top  pins. 


To  compensate  for  the  greater  strains  introduced  by  doubling  the 
length  of  span  and  using  pins  of  longer  stem,  the  diameter  of  the  shank 
of  the  new  pins  was  increased  to  two  inches.  One  line  between  Colgate 


INSULATOR  PINS. 


273 


and  Oakland  is  of  copper,  and  the  other  is  of  aluminum  conductors,  but 
the  same  pins  appear  to  be  used  for  each.  On  the  line  between  Canon 
Ferry  and  Butte,  Mont.,  the  pin  used  in  pole  tops  has  a  shank  i\  inches 
longer  and  J-inch  greater  in  diameter  than  the  pin  used  in  cross-arms. 
The  weakest  pin  included  in  the  table  seems  to  be  that  in  use  on  the  line 
between  Chambly  and  Montreal,  which  is  of  hickory  wood,  about  ij 
inches  in  diameter  at  the  shank,  and  carries  its  No.  oo  copper  wire  8J 
inches  above  the  cross-arm. 

The  following  dimensions  for  standard  wooden  insulator  pins  to  be 
used  on  all  transmission  lines  are  proposed  in  vol.  xxi.,  page  235,  of  the 
Transactions  of  the  American  Institute  of  Electrical  Engineers.  These 
pins  are  designed  to  resist  a  uniform  pull  at  the  smaller  end  and  at  right 
angles  to  the  axis  in  each  case.  The  length  of  each  pin,  in  inches  be- 
tween the  shoulder  and  the  threaded  end,  is  represented  by  L,  and  the 
diameter  of  each  pin  at  its  shank  by  D. 


L. 
i  

D. 

o  87 

L. 

D. 
I  82 

2  

10 

IO 

i  88 

26 

J  J 

•7Q 

I  3 

I-95 

r.  . 

CQ 

TC 

217 

I....:::.::  . 

C.Q 

17 

2  25 

7-  - 

67 

10 

*••*!) 

2  3d 

*:: 

75 

21.  . 

•*  -o^t 

.  2.42 

The  two  strongest  pins  in  Table  II.  appear  to  be  those  in  use  on  the 
line  between  Shawinigan  Falls  and  Montreal  and  on  the  line  from  Niag- 
ara Falls  to  Buffalo.  The  former  have  a  diameter  of  2}  inches  at  the 
shank,  and  the  wire  is  carried  16}  inches  above  the  shoulder  of  the  pin. 
On  the  new  Niagara  line  the  shank  diameter  of  each  pin  is  only  2}  inches, 
but  the  line  wire  is  only  10  inches  above  the  shoulder.  It  was  found  by 
tests  that  a  strain  of  2,100  pounds  at  the  top  of  the  insulator  and  at  right 
angles  to  the  axis  of  this  Niagara  pin  was  necessary  to  break  it  at  the 
shank.  This  strain  is  about  six  times  as  great  as  the  calculated  maxi- 
mum strain  that  will  occur  in  service  on  the  line. 

Some  of  the  pins  here  noted  are  much  stronger  than  those  proposed 
in  the  above  specifications  for  standard  pins.  The  pins  on  the  old  Niag- 
ara line  have  a  shank  diameter  of  2  inches,  with  a  stem  only  5^  inches 
long,  while  the  proposed  pin  of  2  inches  diameter  at  the  shank  has  a 
stem  1 1  inches  long.  On  the  Colgate  and  Oakland  line  a  shank  diameter 
of  2$  inches  goes  with  a  length  of  lof  inches  in  the  stem,  but  the  pro- 
posed pin  with  this  size  of  shank  has  a  stem  13  inches  long.  For  a  shank 


274    ELECTRIC  TRANSMISSION  OF  WATER-POWER.  ^ 

of  2j  inches  diameter  the  proposed  pin  has  a  stem  15  inches  long,  but  the 
pins  with  this  diameter  of  shank  on  the  Electra  line  are  only  12  inches 
long  in  the  stem. 

The  2j-inch  diameter  of  shank  in  the  pins  on  the  new  Niagara  line 
goes  with  a  length  of  only  7!  inches  in  the  stem.  The  new  Niagara  pin 
is  thus  almost  exactly  twice  as  strong  as  the  proposed  pin,  since  the 
strength  of  a  pin  where  the  shank  joins  the  stem  varies  inversely  as  the 
length  of  the  stem,  all  other  factors  being  the  same. 

Pins  on  the  Shawinigan  Falls  line  have  a  shank  2}  inches  in  diameter, 
with  a  length  of  13 J  inches  in  the  stem;  but  the  largest  of  the  proposed 
pins,  that  with  a  stem  19  inches  long,  has  a  diameter  of  only  2^  inches 
in  the  shank. 

It  is  hardly  too  much  to  say  in  the  interest  of  good  engineering  that 
the  wooden  pin  of  about  5  inches  length  of  stem  and  ij  inches  diameter 
of  shank,  as  well  as  all  longer  pins  of  no  greater  strength,  should  be  dis- 
carded for  long  transmission  lines  of  high  voltage.  These  pins  have  done 
good  service  on  telegraph  and  telephone  lines,  and  on  local  lighting  cir- 
cuits of  No.  6  B.  &  S.  gauge  wire  or  smaller,  and  they  may  well  be  left 
for  such  work. 

To  meet  the  conditions  of  transmission  work  a  change  in  both  the 
shape  and  size  of  pins  is  necessary.  In  the  first  place,  the  shoulder  on 
pins  where  the  shank  and  stem  meet,  that  relic  of  telegraph  practice, 
should  be  entirely  discarded.  This  change  will  save  considerable  lumber 
on  pins  of  a  given  diameter  at  the  shank,  and  will  increase  the  strength 
of  the  pin  by  avoiding  the  sharp  corner  at  the  junction  of  the  shank  and 
stem. 

Another  change  of  design  should  leave  an  excess  of  strength  in  the 
stem  of  the  pin,  to  provide  for  deterioration  of  the  wood,  and  particularly 
for  charring  by  current  breakage.  This  increase  of  diameter  and 
strength  near  the  top  of  the  pin  will  cost  nothing  in  lumber,  for  the  wood 
is  necessarily  there  unless  it  is  turned  off.  The  shank  of  each  pin  should 
be  proportionately  shorter  than  in  the  older  type,  and  the  pin  hole  should 
be  bored  only  part  way  through  the  cross-arm.  A  saving  in  lumber  for 
pins  and  for  cross-arms  will  thus  be  made,  since  the  size  of  the  cross-arm 
may  be  less  for  a  given  resistance  to  splitting. 

With  these  changes  in  general  design  the  pin  is  a  simple  cylinder  in 
the  shank,  with  a  gentle  taper  from  the  shank  to  form  the  stem.  An 
example  of  this  design,  which  might  well  serve  as  a  basis  for  a  line  of 
standard  pins,  would  be  a  pin  2  inches  in  diameter  and  3  J  inches  long  in 
the  shank,  and  tapering  for  a  length  of  5  inches  from  the  shank  to  form 
18 


INSULATOR  PINS.  275 

the  stem,  with  a  diameter  of  i^  inches  at  the  top.  The  hole  in  a  cross- 
arm  for  this  pin  should  be  3^  inches  deep,  and  this,  in  an  arm  4}  inches 
deep,  would  leave  i  J  inches  of  wood  below  the  pin.  From  the  lower  end 
of  the  pin  hole,  a  hole  J-inch  in  diameter  should  run  to  the  bottom  of  the 
cross-arm  to  drain  off  water.  A  line  of  longer  pins  designed  to  resist 
the  same  line  pull  as  this  short  one  would  be  strong  enough  for  small 
conductors,  say  up  to  No.  i  B.  &  S.  gauge  wire. 

For  larger  wires,  long  spans  and  sharp  angles  in  a  line,  a  pin  2j 
inches  in  diameter  and  4^  inches  long  in  the  shank,  tapering  for  5  inches 
to  a  diameter  of  if  inches  at  the  top,  or  longer  pins  of  equal  strength, 
should  be  used. 

Where  the  pin  holes  do  not  extend  through  the  cross-arm  there  is  no 
need  of  a  shoulder  on  the  pin  to  sustain  the  weight  of  the  line  wire.  In 
the  cross-arm  on  the  new  Niagara  Falls  line  each  pin  hole  is  bored  to  a 
depth  of  5  inches,  leaving  i  inch  of  wood  below  the  hole.  On  the  line 
from  Electra  to  San  Francisco  the  depth  of  each  pin  hole  is  again  5  inches, 
and  the  depth  of  the  cross-arm  6  inches. 

The  pins  for  use  on  the  Electra  line  were  kept  for  several  hours  in  a 
vat  of  linseed  oil  at  a  temperature  of  210°  F.  The  pins  for  the  Shawini- 
gan  line  were  boiled  in  stearic  acid.  All  wooden  pins  should  be  treated 
chemically,  but  the  object  of  this  treatment  should  be  to  prevent  decay 
rather  than  to  give  them  any  particular  insulating  value. 

The  lack  of  strength  in  wooden  pins  and  their  destruction  in  some 
cases  by  current  leakage  are  leading  to  the  use  of  iron  and  steel  pins.  Such 
a  pin,  in  use  on  the  lines  of  the  Washington  Power  Company,  of  Spokane, 
Wash.,  is  made  up  of  a  mild  steel  bar  17^  inches  long  and  ij  inches  in 
diameter,  cast  into  a  shank  at  one  end,  so  that  the  total  length  is  18  inches. 
The  cast-iron  shank  has  a  diameter  of  2^  inches,  with  a  shoulder  of  2^ 
inches  diameter  at  its  upper  end.  To  prevent  the  pin  from  lifting  out  of 
its  hole  a  small  screw  enters  the  top  of  the  cross-arm  and  bears  on  the 
top  end  of  the  shank.  Above  the  cast-iron  shank  the  length  of  the  steel 
rod  is  1 2  inches,  and  starting  J  inch  down  from  its  top  a  portion  of  the 
rod  J  inch  long  is  turned  to  a  diameter  of  one  inch. 

It  is  said  that  this  pin  begins  to  bend  with  a  pull  of  1,000  pounds  at 
its  top,  but  that  it  will  support  the  insulator  safely  even  when  badly 
bent. 

Insulators  may  resist  puncture  and  prevent  surface  arcing  from  wire 
to  pin,  but  still  allow  a  large  though  silent  flow  of  energy  over  the  pins 
and  cross-arms  between  the  conductors  of  a  transmission  circuit.  The 
rate  at  which  current  flows  from  one  wire  of  a  transmission  circuit  to 


276    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

another  in  this  way  depends  on  the  total  resistance  of  each  path  over 
insulator  surfaces  and  through  air  to  the  pins  and  cross-arm,  and  then 
over  these  parts. 

If  the  pins  and  cross-arm  are  entirely  of  iron,  the  total  resistance  of 
the  path  through  them  from  wire  to  wire  is  practically  that  of  the  insulator 
surfaces.  If  the  pins  and  cross-arm  are  of  wood  which  is  dry,  they  may 
offer  an  appreciable  part  of  the  total  resistance  of  the  path  through  them 
between  the  wires  of  a  circuit ;  but  if  the  wood  be  wet,  its  resistance  is 
very  much  reduced. 

The  resistance  of  wooden  pins  and  cross-arm  may  be  so  small  com- 
pared with  that  of  the  air  and  insulator  surfaces  that  complete  the  path 
through  them  from  wire  to  wire  of  a  circuit,  that  the  effect  of  these  wooden 
parts  in  checking  the  flow  of  current  between  conductors  is  relatively 
unimportant,  and  yet  the  resistances  of  these  pins  and  the  cross-arm 
may  affect  their  lasting  qualities. 

The  current  that  flows  over  the  pins  and  cross-arms  from  one  wire 
to  another  of  a  high-tension  circuit  may  be  so  small  as  not  to  injure  these 
wooden  parts  when  evenly  distributed  over  them,  and  yet  this  same  cur- 
rent may  char  or  burn  the  wood  if  confined  to  a  narrow  path.  Such  a 
leakage  current  will  naturally  cease  to  be  evenly  distributed  over  pins 
and  their  cross-arms  when  certain  portions  of  their  surfaces  are  of  much 
lower  resistance  than  others,  because  an  electric  current  divides  and  fol- 
lows several  possible  paths  in  the  inverse  ratio  of  their  resistances. 

These  narrow  paths  of  relatively  low  resistance  along  wooden  pins 
and  cross-arms  are  heated  and  charred  by  the  very  current  that  they 
attract,  so  that  the  conductivity  of  the  path  and  the  heat  developed 
therein  react  mutually  to  increase  each  other,  and  tend  toward  the  de- 
struction of  the  wood. 

Among  causes  that  tend  to  make  some  parts  of  pins  and  cross-arms 
better  conductors  than  others,  there  may  be  mentioned  cracks  in  the 
wood,  where  dirt  and  moisture  collect,  dust,  with  a  mixture  of  salt  de- 
posited on  the  wood  by  the  winds  at  certain  places,  and  sea  fogs  that  are 
often  blown  only  against  one  side  of  the  pins  and  arms  and  deposit  salt. 

To  make  matters  worse,  the  same  cause  that  creates  a  path  of  rela- 
tively good  conductivity  along  wooden  pins  and  cross-arms  often  materi- 
ally lowers  the  resistance  offered  to  the  leakage  of  current  by  the  insulator 
surfaces.  Thus  an  increase  of  the  rate  at  which  energy  passes  from 
wire  to  wire  of  a  circuit,  and  the  concentration  of  this  energy  in  certain 
parts  of  the  wooden  path,  are  sometimes  brought  about  at  the  same 
time.  Where  the  line  insulators  employed  are  so  designed  that  the  re- 


INSULATOR  PINS.  277 

sistance  of  the  dry  wooden  pins  and  cross-arms  forms  a  material  part  of 
the  total  resistance  between  the  wires  of  a  circuit,  a  rain  or  heavy  fog  may 
cause  a  very  large  increase  in  the  rate  at  which  energy  passes  over  these 
wooden  parts  between  the  conductors. 

As  long  as  only  moderate  voltages  were  carried  on  line  conductors, 
the  charring  and  burning  of  their  pins  and  cross-arms  was  a  very  unusual 
matter;  but  with  the  application  of  very  high  pressures  on  long  circuits 
the  destruction  of  these  wooden  parts  by  the  heat  of  leakage  currents  has 
become  a  serious  menace  to  transmission  systems.  Even  with  low  volt- 
ages there  may  be  charring  and  burning  of  pins  and  cross-arms  if  the  line 
insulators  are  very  poor  or  if  the  conditions  as  to  weather  and  flying  dust 
are  sufficiently  severe. 

In  vol.  xx.  of  the  Transactions  of  the  American  Institute  of  Electrical 
Engineers,  pages  435  to  442  and  471  to  479,  an  account  of  the  charring 
and  burning  of  pins  on  several  transmission  lines  is  given,  from  which 
some  of  the  following  examples  are  taken. 

In  one  case  a  line  that  ran  near  a  certain  chemical  factory  was  said 
to  be  much  troubled  by  the  burning  of  its  pins,  though  the  voltage  em- 
ployed was  only  440,  and  the  insulators  were  designed  for  circuits  of 
10,000  volts.  In  rainy  weather,  when  insulators,  pins,  and  cross-arms 
were  washed  clear  of  the  chemical  deposits,  there  was  no  pin  burning. 
Similar  trouble  has  been  met  with  on  sections  of  the  4o,ooo-volt  Provo 
line,  in  Utah,  where  dust,  mixed  with  salt,  is  deposited  on  the  insulators, 
pins,  and  cross-arms.  On  page  708  a  2,000- volt  line  is  mentioned  on 
which  fog,  dust,  and  rain  caused  much  burning  of  pins. 

.  When  circuits  are  operated  at  voltages  of  40,000  to  60,000,  no  very 
severe  climatic  conditions  are  necessary  to  develop  serious  trouble  in  the 
wooden  pins  by  leakage  currents,  even  where  the  transmission  lines  are 
supported  in  insulators  of  the  largest  and  best  types  yet  developed. 
Striking  examples  along  this  line  may  be  seen  in  the  transmission  systems 
between  Colgate  and  Oakland,  Cal.,  and  between  Electra  and  San  Fran- 
cisco. Both  of  these  systems  were  designed  to  transmit  energy  at  60,000 
volts,  but  the  actual  pressure  of  operation  seems  to  have  been  limited  to 
about  40,000  volts  during  much  of  their  period  of  service. 

Insulators  of  a  single  type  and  size  are  used  on  both  of  these  transmis- 
sion lines,  and  are  among  the  largest  ever  put  into  service  on  long  cir- 
cuits. Each  of  these  insulators  is  n  inches  in  diameter,  and  nj  inches 
high  from  the  lower  edge  to  the  top,  the  line  wire  being  carried  in  a 
central  top  groove.  The  wooden  pins  used  on  the  two  lines  vary  a  little 
in  size,  so  that  on  the  Electra  line  each  pin  stands  nj  inches  above  its 


278    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

cross-arm,  while  on  the  Colgate  line  the  corresponding  distance  is  12 
inches.  As  the  insulators  are  of  the  same  size  in  each  case,  the  length  of 
the  pin  between  the  lower  edge  of  each  insulator  and  the  top  of  the 
cross-arm  is  4  inches  on  the  Colgate  line  and  3 finches  on  the  Electra  line. 

On  the  latter  line  a  porcelain  sleeve,  entirely  separate  from  and  mak- 
ing no  contact  with  the  insulator,  covers  each  pin  from  the  top  of  its 
cross-arm  to  a  point  above  the  lower  edge  of  the  insulator.  On  the  Col- 
gate line  each  insulator  makes  contact  with  its  pin  for  a  length  of  2^ 
inches  down  from  the  top  of  its  thread,  and  on  the  Electra  line  the  contact 
of  each  insulator  with  its  pin  runs  down  3^  inches  below  the  top  of  the 
thread.  This  leaves  9  inches  in  the  length  of  the  pin  between  the  insula- 
tor contact  and  the  top  of  each  cross-arm  on  the  Colgate  line,  and  a  cor- 
responding length  of  pin  amounting  to  8  J  inches  on  the  Electra  line.  Of 
this  8.i  inches  of  pin  surface,  about  6  inches  is  covered  by  the  porcelain 
insulating  sleeve  used  on  each  pin  of  the  Electra  line,  so  that  only  about 
2\  inches  of  the  length  of  each  pin  on  that  line  is  exposed  to  the  leakage 
of  current  from  the  insulator  directly  through  the  air.  Both  the  sizes  of 
pins  just  mentioned  were  made  of  eucalyptus  wood,  boiled  in  linseed  oil. 

Each  one  of  three  pins  taken  from  a  pole,  between  North  Tomer 
and  Cordelia,  on  the  Colgate  line,  was  badly  charred  and  burned 
on  its  side  that  faced  the  damp  ocean  winds.  This  charring  extended 
all  the  way  down  each  pin  from  the  point  where  the  insulator  made  con- 
tact with  it,  a  little  under  the  threads,  to  the  top  of  the  cross-arm  nine 
inches  below.  Two  of  these  pins  were  located  at  the  opposite  ends  of  a 
cross-arm,  and  the  third  was  fixed  in  the  top  of  the  pole.  This  cross-arm 
was  charred  or  burnt,  as  well  as  the  pin,  but  no  defects  could  be  detected 
in  the  insulators  that  the  pins  supported. 

As  to  these  three  pins,  the  most  reasonable  explanation  seems  to  be 
that  enough  current  leaked  over  both  the  outside  and  inside  surfaces  of 
each  insulator  and  through  the  air  to  char  the  pin  and  cross-arm.  In 
flowing  down  each  pin,  the  current  was  naturally  concentrated  on  the 
side  exposed  to  the  damp  winds  of  the  ocean,  because  the  deposit  of 
moisture  by  these  winds  lowered  the  resistance  on  that  side.  When  these 
winds  were  not  blowing,  and  before  a  pin  became  charred  on  one  side, 
its  resistance  was  probably  about  the  same  all  the  way  around,  and  the 
leakage  current,  being  distributed  over  the  pin,  was  not  sufficient  to  char 
it.  The  damp  wind  would,  of  course,  lower  the  surface  resistance  of 
each  insulator,  and  this,  with  the  deposit  of  moisture  on  the  pins  and 
cross-arm,  many  have  made  a  very  material  reduction  in  the  total  resist- 
ance from  wire  to  wire. 


INSULATOR  PINS.  279 

The  insulators  used  on  these  pins  each  had  two  petticoats,  an  upper 
one,  ii  inches  in  diameter,  and  a  lower  one,  6J  inches  in  diameter,  the 
lower  edge  of  the  smaller  petticoat  being  yi  inches  beneath  the  lower 
outside  edge  of  the  larger  petticoat.  As  the  inner  surface  of  the  larger 
petticoat  was  much  nearer  to  a  horizontal  plane  than  the  inner  surface 
of  the  smaller  petticoat,  moisture  would  have  been  more  readily  retained 
on  it,  and  the  greater  part  of  the  surface  resistance  of  the  insulator  during 
wet  weather  must  therefore  have  been  on  the  inside  of  the  smaller  petti- 
coat. At  its  lower  edge  the  smaller  petticoat  was  distant  radially  about 
if  inches  from  the  pin,  and  the  distance  between  the  pin  and  the  inside 
surface  of  the  smaller  petticoat  gradually  decreased  to  actual  contact  at 
a  point  5^  inches  above  this  lower  edge. 

The  path  of  the  current  from  the  line  wire  to  the  pin  in  this  case  seems 
to  have  been  first  over  the  entire  insulator  surface  to  the  lower  edge  of 
the  smaller  petticoat  and  then  partly  up  over  the  inner  surface  of  this 
petticoat  and  partly  from  that  surface  through  the  air.  On  each  of  these 
three  pins  the  charring  was  quite  as  bad  just  below  the  thread  as  it  was 
further  down,  so  that  a  large  part  of  the  leakage  current  seems  to  have 
gone  up  over  the  interior  surface  of  the  smaller  petticoat.  The  charred 
portion  of  these  pins  extended  but  little,  if  at  all,  into  the  threads  near 
the  tops  or  into  the  part  of  the  pin  fitting  into  the  cross-arm.  The  pres- 
ervation of  the  part  of  each  pin  that  entered  the  cross-arm  seems  to  have 
been  due  to  the  increase  of  surface  and  decrease  of  resistance  of  the 
cross-arm  in  comparison  with  the  pin.  Preservation  of  the  threaded  part 
of  each  pin  seems  to  have  been  due  to  its  protection  from  moisture  and 
its  high  resistance,  so  that  little  or  no  current  passed  over  it. 

Another  pin  taken  from  the  same  line  as  the  three  just  considered  was 
badly  burned  at  a  point  about  1.75  inches  below  the  threads,  but  on  sawing 
it  completely  across  at  two  points  below  the  charred  spot  the  entire  sec- 
tion was  found  to  be  perfectly  sound  and  free  from  any  sign  of  burning. 
The  explanation  of  the  condition  of  this  pin  is,  perhaps,  that  the  resist- 
ance of  the  burned  part,  owing  to  its  additional  protection  and  dryness, 
was  high  compared  with  that  of  the  lower  part  of  the  pin,  and  thus  de- 
veloped most  of  the  heat  on  the  passage  of  current.  It  is  not  clear,  how- 
ever, why  this  pin  should  burn  only  just  below  the  thread,  while  other 
pins  of  the  same  kind  on  the  same  line  were  charred  all  the  way  down 
from  the  thread  to  the  cross-arm. 

Another  curious  result  noticed  in  some  pins  on  this  same  line  is  the 
softening  of  the  threads  so  that  they  can  be  rubbed  off  with  the 
fingers. 


280    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 
RELATION  OF  PINS  AND  INSULATORS. 


Location  of  Line. 

Voltage  of 
Line. 

Diameter  of 
Insulator. 

21 
|9 

O>  tn 

Length  of  Pin 
Covered  by 
Insulator. 

Electra  to  San  Francisco  .  .  . 

60  ooo 

Inches. 

Inches. 

Inches. 

12 

Colgate  to  Oakland.  

60  ooo 

1  1 

ill 

8 

Canon  Ferry  to  Butte  .  .  . 

^o  ooo 

12 

Shawinigan  Falls  to  Montreal  .    . 

"50,000 

10 

I  3 

lof 

Santa  Ana  River  to  Los  Angeles  
Provo  around  Utah  Lake 

33,000 
40  ooo 

7 

Spier  Falls  to  Schenectady 

10  ooo 

uj 

rl 

Niagara  Falls  to  Buffalo. 

22  OOO 

7* 

7" 

The  softened  wood  of  the  threads  is  not  charred,  but  is  said  to  have 
a  sour  taste  and  to  resemble  digested  wood  pulp.  While  the  threads  of 
a  wooden  pin  are  destroyed  in  this  way  the  remainder  of  the  pin  may  still 
remain  perfect  and  show  no  charring. 

RELATIONS  OF  PINS  AND  INSULATORS. 


Location  of  Line. 

Length  of  Pin 
Between 
Insulator  and 
Cross-arm. 

Distance  from 
Outer  Pettitoat 
to  Pin 
Through  Air. 

Distance  from 
Lowest  Pet- 
ticoat to  Pin 
Through  Air. 

Electra  to  San  Francisco  

Inches, 
o 

Inches. 

iol 

Inches. 

3i 

Colgate  to  Oakland  

si 

IO 

»i 

Canon  Ferry  to  Butte  

i* 

o 

i£ 

Shawinigan  Falls  to  Montreal 

31 

91 

Santa  Ana  River  to  Los  Angeles  
Provo  around  Utah  Lake  .  .  . 

3i 

•1 

2J 

"2\ 

Spier  Falls  to  Schenectady  ....    . 

4 

i 

Niagara  Falls  to  Buffalo  

•J 

A\ 

2 

In  explanation  of  this  disintegration  of  the  threads  of  wooden  pins  it 
was  stated  that  a  number  of  these  pins,  the  tops  of  which  were  reduced 
to  a  white  powder,  had  been  taken  from  the  line  between  Niagara  Falls 
and  Buffalo,  on  which  the  voltage  is  22,000,  and  that  this  powder  proved 
on  analysis  to  be  a  nitrate  salt.  This  salt  was  thought  to  be  the  result 
of  the  action  of  nitric  acid  on  the  wood,  it  being  supposed  that  the  acid 
was  formed  by  a  static  discharge  acting  on  the  oxygen  and  nitrogen  of 


INSULATOR  PINS.  281 

the  air  between  the  threads  of  the  insulator  and  pin.  In  support  of  this 
view  it  was  stated  that  an  experimental  line  of  galvanized-iron  wire  at 
Niagara  Falls,  which  was  operated  at  75,000  volts  continuously  during 
nearly  four  months,  turned  black  over  its  entire  length  of  about  two  miles. 
This  surface  disintegration  was  not  due  to  the  normal  action  of  the  air, 
for  similar  wire  at  the  same  place  remained  bright  when  not  used  as  an 
electrical  conductor. 

These  facts  seemed  to  indicate  that  the  brush  discharge  from  the 
wires  carrying  the  7 5,000- volt  current  developed  nitric  acid  from  the 
oxygen  and  nitrogen  of  the  air,  and  that  this  acid  attacked  the  wire. 

One  of  the  above-mentioned  pins  used  on  the  Electra  line  was  much 
charred  and  burned  away  at  a  point  a  little  below  the  threads.  The 
charred  path  of  the  current  could  also  be  traced  down  the  side  of  the  pin 
to  the  cross-arm,  but  this  path  was  not  as  badly  burned  as  the  spot  near 
the  top  of  the  pin. 

A  composite  pin  from  a  3 3,000- volt  line,  probably  a  part  of  the  trans- 
mission system  between  the  Santa  Ana  River  and  Los  Angeles,  was 
burned  through  its  wooden  threads  to  the  central  iron  bolt,  along  a  nar- 
row strip  at  one  side.  Every  pin  burned  on  this  line  was  said  to  show 
the  effects  of  the  current  in  the  way  just  described,  but  no  cross-arms 
were  burned  and  very  few  insulators  punctured. 

The  composite  pin  was  made  up  of  a  central  iron  bolt  19!  inches 
long,  J-inch  in  diameter,  and  with  a  thin  head  above  the  wooden  threads, 
a  sleeve  of  wood  2f  inches  long  and  i  inch  in  diameter  in  its  threaded 
portion,  and  a  sleeve  of  porcelain  3^  inches  long  and  i  J  inches  in  diam- 
eter at  its  upper  and  2yi  inches  at  its  lower  end.  The  sleeves  of  wood 
and  porcelain  were  slipped  over  the  central  iron  bolt  so  that  the  portions 
of  the  pin  above  the  cross-arm  measured  5!  inches.  In  this  case  the 
path  of  the  leakage  current  seems  to  have  been  over  both  the  exterior  and 
interior  surface  of  the  insulator  and  then  through  the  wooden  sleeve  to 
the  central  bolt  and  the  cross-arm. 

The  facts  just  outlined  certainly  indicate  a  serious  menace  to  the  per- 
manence and  reliability  of  long,  high-voltage  transmission  lines  sup- 
ported by  insulators  on  wooden  pins.  If  such  results  have  been  encoun- 
tered on  the  lines  above  named,  where  some  of  the  largest  and  best 
designs  of  insulators  are  employed,  it  is  only  fair  to  assume  that  similar 
destructive  effects  of  leakage  currents  are  taking  place  on  many  other 
lines  that  operate  at  high  voltages. 

It  seems  at  least  doubtful  whether  any  enlargement  or  improvement 
of  the  insulators  themselves  will  entirely  avoid  the  destruction  of  their 


282     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

wooden  pins  in  one  of  the  ways  mentioned.  It  is  probable,  but  not  cer- 
tain, that  further  extension  of  distances  through  air  and  over  insulator 
surfaces,  both  exterior  and  interior,  between  line  wires  and  wooden  pins, 
will  prevent  charring  and  burning  of  the  latter  by  leakage  currents. 
Much  has  already  been  done  in  the  way  of  covering  most  of  the 
pin  above  its  cross-arm  with  the  insulator  parts,  but  even  those  por- 
tions of  the  pin  that  are  best  protected  in  this  way  are  not  free  from 
burning. 

Thus,  on  the  Colgate  line,  eight  inches  of  each  pin  is  protected  by 
the  interior  surface  of  its  insulator,  but  these  pins  were  charred  quite  as 
badly  where  best  protected,  up  close  to  the  thread,  as  they  were  down 
near  the  cross-arm.  The  same  is  true  of  the  Electra  line,  where  a  porce- 
lain sleeve  runs  up  about  the  pin  from  the  cross-arm  to  a  point  above 
the  inner  petticoat  of  each  insulator,  so  that  the  entire  length  of  the  pin 
above  the  cross-arm  is  protected.  On  the  Canon  Ferry  line,  a  glass 
sleeve  that  virtually  forms  a  part  of  each  insulator,  though  mechanically 
separate  from  it,  protects  the  pin  from  its  threaded  portion  to  within  1.5 
inches  of  the  cross-arm. 

Insulators  on  the  line  from  Shawinigan  Falls  to  Montreal  are  each  13 
inches  long  and  extend  down  over  the  pin  to  within  1.5  inches  of  the 
cross-arm.  The  burned  portion  of  each  pin  from  the  Santa  Ana  line 
was  that  carrying  the  threads,  and  thus  in  actual  contact  with  that  part 
of  the  insulator  which  was  separated  by  the  greatest  surface  distance 
from  the  line  wire. 

Aside  from  the  burning  of  pins  is  the  destruction  of  their  threaded 
parts  by  some  chemical  agency  that  is  developed  inside  of  the  tops  of 
the  insulators,  as  shown  in  the  cases  of  the  Colgate  and  Niagara  lines. 
It  does  not  appear  that  any  improvement  of  insulators  will  necessarily 
prevent  chemical  action. 

Though  it  may  not  be  practicable  to  so  increase  the  surface  resistance 
of  each  insulator  that  the  burning  of  wooden  pins  by  leakage  current  will 
be  prevented,  the  substitution  of  a  conducting  for  an  insulating  pin  may 
remedy  the  trouble.  As  the  insulators,  pins,  and  cross-arm  form  a  path 
for  the  leakage  current  from  wire  to  wire,  the  wooden  pins  by  their  re- 
sistance, especially  when  dry,  must  develop  heat.  In  pins  of  steel  or 
iron  this  heat  would  be  trifling  and  would  do  no  damage.  With  pins 
of  good  conducting  material,  like  iron,  the  amount  of  leakage  from  wire 
to  wire,  with  a  given  design  of  insulator,  would,  no  doubt,  be  somewhat 
greater  than  the  leakage  with  wooden  pins. 

It  will  be  cheaper,  however,  to  increase  the  resistance  of  new  insulators 


INSULATOR  PINS.  283 

up  to  the  combined  resistance  of  present  insulators  and  their  wooden 
pins  than  it  will  be  to  replace  these  pins  when  they  are  burned. 

From  all  the  evidence  at  hand,  it  seems  that  insulators  which  reduce 
the  leakage  of  current  over  their  surfaces  to  permissible  limits  as  far  as 
mere  loss  of  energy  is  concerned,  even  with  iron  pins,  will  not  prevent 
the  charring  and  destruction  of  wooden  pins. 

When  any  suitable  insulator  is  dry  and  clean  it  offers  all  necessary 


FIG.  90.— Glass  Insulator  and  Sleeve  on  5o,ooo-volt  Line  Between  Caflon  Ferry 
and  Butte,  Mont, 

resistance  to  the  leakage  of  current  over  its  surface,  and  any  resistance 
in  the  pin  that  carries  the  insulator  is  of  small  importance.  If  the  resist- 
ance of  an  insulator  needs  to  be  reinforced  by  that  of  its  pin  in  any  case, 
it  is  when  the  surface  of  the  insulator  is  wet  or  dirty.  Unfortunately, 
however,  the  same  weather  conditions  that  deposit  dirt  or  moisture  on 
an  insulator  make  similar  deposits  on  its  pin,  and  the  resistance  of  the 
pin  is  lowered  much  more  than  that  of  the  insulator  by  such  deposits. 
The  increase  of  current  leakage  over  the  surface  of  an  insulator  during 
rains  and  fogs  usually  does  no  damage  to  the  insulator  itself,  but  such 
leakage  over  the  wet  pin  soon  develops  a  surface  layer  of  carbon  that 
continues  to  act  as  a  good  conductor  after  the  moisture  that  temporarily 


284     ELECTRIC  TRANSMISSION  OF  WATER-POWER.. 

lowered  the  resistance  has  gone.  Reasons  like  these  have  led  some  engi- 
neers to  prefer  iron  pins  with  insulators  that  offer  all  of  the  resistance 
necessary  for  the  voltage  employed  on  the  line. 

It  may  be  suggested  that  the  use  of  iron  pins  will  transfer  the  charring 
and  burning  to  the  wooden  cross-arms,  but  this  does  not  seem  to  be  a 
necessary  result.  The  comparative  freedom  of  cross-arms  from  charring 
and  burning  where  wooden  pins  are  used  seems  to  be  due  to  the  larger 
surface  and  lower  resistance  of  the  cross-arms.  With  iron  pins  having 
a  shank  of  small  diameter,  so  that  the  area  of  contact  surface  between  the 
pin  and  the  wooden  cross-arm  is  relatively  small,  there  may  be  some 
charring  of  the  wood  at  this  contact  surface.  Should  it  be  thought  de- 
sirable to  guard  against  any  trouble  of  this  sort,  the  surface  of  the  iron 
pin  in  contact  with  the  cross-arm  may  be  made  ample  by  the  use  of 
large  washers,  or  by  giving  each  pin  a  greater  diameter  at  the  shank  than 
elsewhere. 

It  may  be  noted  that  the  pins  with  a  central  iron  bolt  only  half  an 
inch  in  diameter,  that  were  used  on  the  3 3,000- volt  Santa  Ana  line,  were 
said  to  have  caused  no  burning  of  their  cross-arms  in  those  cases  in  which 
the  wooden  threads  about  the  top  of  the  central  bolt  were  burned  through. 

Another  possible  trouble  with  iron  pins  is  that  they,  by  their  greater 
rate  of  expansion  than  glass  or  porcelain,  will  break  their  insulators. 
Such  results  can  readily  be  avoided  by  cementing  each  iron  pin  into  its 
insulator,  instead  of  screwing  the  insulator  onto  the  pin.  Iron  pins  will, 
no  doubt,  cost  somewhat  more  than  those  of  wood,  but  this  cost  will 
in  any  event  be  only  a  small  percentage  of  the  total  investment  in  a 
transmission  line.  Considering  the  cost  of  the  renewals  of  wooden 
pins,  there  seems  little  doubt  that  on  a  line  where  the  voltage  and  other 
conditions  are  such  as  to  result  in  frequent  burning,  iron  pins  would  be 
cheaper  in  the  end. 

Iron  pins  have  already  been  adopted  on  a  number  of  high-voltage 
lines.  Not  only  iron  pins,  but  even  iron  cross-arms  and  iron  poles  are 
in  use  on  a  number  of  transmission  lines.  On  a  long  line  now  under 
construction  in  Mexico,  iron  towers,  placed  as  much  as  400  feet  apart, 
are  used  instead  of  wooden  poles,  and  both  the  pins  and  cross-arms  are 
also  of  iron.  The  75-mile  line  from  Niagara  Falls  to  Toranto  is  carried 
entirely  on  steel  towers. 

The  Vancouver  Power  Company,  Vancouver,  British  Columbia,  use 
a  pin  that  consists  of  a  steel  bolt  about  1 2  inches  long  fitted  with  a  sleeve 
of  cast  iron  4^  inches  long  to  enter  the  cross-arm,  and  a  lead  thread  to 
screw  into  the  insulator.  On  the  1 1  i-mile  line  of  the  Washington  Power 


INSULATOR  PINS. 


Company,  of  Spokane,  which  was  designed  to  operate  at  60,000  volts  and 
runs  to  the  Standard  and  Hecla  mines,  a  pin  consisting  of  a  steel  bar  i  J 
inches  in  diameter,  with  a  cast-iron  shank  2yV  inches  in  diameter  to 
enter  the  cross-arm,  and  with  the  lead  threads  for  the  insulator,  is  used. 
On  the  network  of  transmission  lines  between  Spier  Falls,  Schenec- 
tady,  Albany,  and  Troy,  in  the  State  of  New  York,  the  insulators  are 
supported  on  iron  pins  of  two  types.  One  of  these  pins,  used  at  corners 
and  where  the  strain  on  the  wire  line  is  exceptionally  heavy,  is  made  up 


FIG.  92— Iron  Pins  on  Spier  Falls  Line. 

of  a  wrought-iron  bolt  j-inch  in  diameter  and  i6j  inches  long  over  the 
head,  and  of  a  malleable  iron  casting  8}  inches  long.  This  casting  has  a 
flange  of  5  by  3!  inches  at  its  lower  end  that  rests  on  the  top  of  the  cross- 
arm,  and  the  bolt  passes  from  the  top  of  the  casting  down  through  it  and 
the  cross-arm.  Threads  are  cut  on  the  lower  end  of  the  bolt,  and  a  nut 
and  washer  secure  it  in  the  cross-arm.  The  total  height  of  this  pin  above 
the  cross-arm  is  gj  inches. 

For  straight  work  on  this  line  a  pin  with  stem  entirely  of  malleable 
iron,  and  a  bolt  that  comes  up  through  the  cross-arm  and  enters  the  base 
of  the  casting,  is  used.  The  cast  top  of  this  pin  has  four  vertical  webs, 


286    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

and  its  rectangular  base,  which  rests  on  the  top  of  the  cross-arm,  is  3  J 
by  4  inches.  The  bolt  that  comes  up  through  the  cross-arm  and  taps 
into  the  base  of  the  casting  is  {-inch  in  diameter.  The  cast  part  of  this 
pin  has  such  a  length  that  the  top  of  its  insulator  is  carried  lof  inches 
above  the  cross-arm.  For  the  casting  the  length  is  gj  inches. 

Both  of  the  types  of  iron  pins  in  use  on  the  Spier  Falls  lines  are  se- 
cured to  their  insulators  with  Portland  cement  poured  into  the  pin  hole 
while  liquid  when  the  insulator  is  upside  down  and  the  pin  is  held  cen- 


FIG.  93— Standard  Pin,  Toronto  and  Niagara  Line. 

trally  in  its  hole.    The  top  of  each  casting  is  smaller  in  diameter  than  the 
hole  in  the  insulator,  and  is  grooved  so  as  to  hold  the  cement. 

On  a  long  line  designed  for  60,000  volts,  and  recently  completed  in 
California,  wooden  pins  are  used  with  porcelain  insulators,  each  14  inches 
in  diameter  and  1 2^  inches  high.  Each  of  these  pins  is  entirely  covered 
with  sheet  zinc  from  the  cross-arm  to  the  threaded  end,  and  it  is  expected 
that  this  metal  covering  will  protect  the  wood  of  the  pin  from  injury  by 
the  leakage  current. 


CHAPTER  XXI. 

INSULATORS  FOR  TRANSMISSION  LINES. 

LINE  insulators,  pins,  and  cross-arms  all  go  to  make  up  paths  of 
more  or  less  conductivity  between  the  wires  of  a  transmission  circuit. 
The  amount  of  current  flowing  along  these  paths  from  one  conductor 
to  another  in  any  case  will  depend  on  the  combined  resistance  of  the 
insulators,  pins,  and  cross-arm  at  each  pole. 

As  a  general  rule,  the  wires  of  high-voltage  transmission  circuits  are 
used  bare  because  continuous  coverings  would  add  materially  to  the  cost 
with  only  a  trifling  increase  in  effective  insulation  against  high  volt- 
ages. In  some  instances  the  wires  of  high-pressure  transmission  lines 
have  individual  coverings  for  short  distances  where  they  enter  cities, 
but  often  this  is  not  the  case.  At  Manchester,  N.  H.,  bare  conductors 
from  water-power  plants  enter  the  sub-station,  well  within  the  city  limits, 
at  12,000  volts.  From  the  water-power  at  Chambly  the  bare  25,000- 
volt  circuits,  after  crossing  the  St.  Lawrence  River  over  the  great  Victoria 
bridge,  pass  overhead  to  a  terminal-house  near  the  water-front  in  Mont- 
real. In  order  to  reach  the  General  Electric  Works,  the  30,ooo-volt 
circuits  from  Spier  Falls  enter  the  city  limits  of  Schenectady,  N.  Y., 
with  bare  overhead  conductors. 

Where  transmission  lines  pass  over  a  territory  exposed  to  corrosive 
gases,  it  is  sometimes  desirable  to  give  each  wire  a  weather-proof  cover- 
ing. An  instance  of  this  sort  occurs  near  Niagara  Falls  where  the 
aluminum  conductors  forming  one  of  the  circuits  to  Buffalo  are  covered 
with  a  braid  that  is  saturated  with  asphaltum  for  some  distance. 

Each  path,  formed  by  the  surface  of  the  insulators  of  a  line  and  the 
pins  and  cross-arm  by  which  they  are  supported,  not  only  wastes  the 
energy  represented  by  the  leakage  current  passing  over  it,  but  may  lead 
to  the  charring  and  burning  of  the  pins  and  cross-arm  by  this  current. 
To  prevent  such  burning,  the  main  reliance  is  to  be  placed  in  the 
surface  resistance  of  the  insulators  rather  than  that  of  pins  and  cross- 
arms.  These  insulators  should  be  made  of  glass  or  porcelain,  and 
should  be  used  dry — that  is,  without  oil.  In  some  of  the  early  trans- 
mission lines,  insulators  were  used  on  which  the  lower  edges  were 

287 


288    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

turned  inward  and  upward  so  that  a  circular  trough  was  formed 
beneath  the  body  of  the  insulator,  and  this  trough  was  filled  with 
heavy  petroleum.  It  was  found,  however,  that  this  trough  of  oil 
served  to  collect  dirt  and  thus  tended  to  lower  the  insulation  between 
wire  and  cross-arm,  so  that  the  practice  was  soon  abandoned.  Glass 
and  porcelain  insulators  are  rivals  for  use  on  high-tension  lines,  and  each 
has  advantages  of  its  own.  Porcelain  insulators  are  much  stronger 
mechanically  than  are  those  of  glass,  and  are  not  liable  to  crack  because 
of  unequal  internal  expansion,  a  result  sometimes  met  with  where  glass 
insulators  are  exposed  to  a  hot  morning  sun.  In  favor  of  glass  insulators 
it  may  be  said  that  their  insulating  properties  are  quite  uniform,  and 
that,  unlike  porcelain,  their  internal  defects  are  often  apparent  on 
inspection.  In  order  to  avoid  internal  defects  in  large  porcelain  insula- 
tors, it  has  been  found  necessary  to  manufacture  some  designs  in  several 
parts  and  then  cement  the  parts  of  each  insulator  together. 

Defective  insulators  may  be  divided  into  two  classes — those  that  the 
line  voltage  will  puncture  and  break  and  those  that  permit  an  excessive 
amount  of  current  to  pass  over  their  surfaces  to  the  pins  and  cross-arms. 
Where  an  insulator  is  punctured  and  broken,  the  pin,  cross-arm,  ami 
pole  to  which  it  is  attached  are  liable  to  be  burned  up.  If  the  leakage 
of  current  over  the  surface  of  an  insulator  is  large,  not  only  may  the  loss 
of  energy  on  the  line  where  the  insulator  is  used  be  serious,  but  this 
energy  follows  the  pins  and  cross-arm  in  its  path  from  wire  to  wire,  and 
gradually  chars  the  former,  or  both,  so  that  they  are  ultimately  set  on 
fire  or  break  through  lack  of  mechanical  strength.  The  discharge  over 
the  surface  of  an  insulator  may  be  so  large  in  amount  as  to  have  a  dis- 
ruptive character,  and  thus  to  be  readily  visible.  More  frequently  this 
surface  leakage  of  current  over  insulators  is  of  the  invisible  and  silent 
sort  that  nevertheless  may  be  sufficient  in  amount  to  char,  weaken,  and 
even  ultimately  set  fire  to  pins  and  cross-arms. 

All  insulators,  whether  made  of  glass  or  porcelain,  should  be  tested 
electrically  to  determine  their  ability  to  resist  puncture,  and  to  hold  back 
the  surface  leakage  of  current,  before  they  are  put  into  practical  use  on 
high-tension  lines.  Experience  has  shown  that  inspection  alone  cannot  be 
depended  on  to  detect  defective  glass  insulators.  Electrical  testing  of  insu- 
lators serves  well  to  determine  the  voltage  to  which  they  may  be  subjected 
in  practical  service  with  little  danger  of  puncture  by  the  disruptive  passage 
of  current  through  their  substance.  It  is  also  possible  to  determine  the 
voltage  that  will  cause  a  disruptive  discharge  of  current  over  the  surface 
of  an  insulator,  when  the  outer  part  of  this  surface  is  either  wet  or  dry. 


INSULATORS  FOR  TRANSMISSION  LINES.          289 

This  is  as  far  as  electrical  tests  are  usually  carried,  but  it  seems  desirable 
that  such  tests  should  also  determine  the  amount  of  silent,  invisible  leak- 
age over  the  surface  of  insulators  both  when  they  are  wet  and  when  they 
are  dry,  at  the  voltage  which  their  circuits  are  intended  to  carry.  Such 
a  test  of  silent  leakage  is  important  because  this  sort  of  leakage  chars 
and  weakens  insulator  pins,  and  sets  fire  to  them  and  cross-arms,  be- 
sides representing  a  waste  of  energy. 

The  voltage  employed  to  test  insulators  should  vary  in  amount 
according  to  the  purpose  for  which  any  particular  test  is  made.  Glass 
and  porcelain,  like  many  other  solid  insulators,  will  withstand  a  voltage 
during  a  few  minutes  that  will  cause  a  puncture  if  continued  indefinitely. 
In  this  respect  these  insulators  are  unlike  air,  which  allows  a  disruptive 
discharge  at  once  when  the  voltage  to  which  it  is  exposed  reaches  an 
amount  that  the  air  cannot  permanently  withstand.  Because  of  this 
property  of  glass  and  porcelain  insulators,  it  is  necessary  in  making  a 
puncture  test  to  employ  a  voltage  much  higher  than  that  to  which  they 
are  to  be  permanently  exposed.  In  good  practice  it  is  thought  desirable 
to  test  insulators  for  puncture  with  at  least  twice  the  voltage  of  the  cir- 
cuits which  they  will  be  required  to  permanently  support  on  transmis- 
sion lines. 

For  the  first  transmission  line  from  Niagara  Falls  to  Buffalo,  which 
was  designed  to  operate  at  11,000  volts,  the  porcelain  insulators  were 
tested  for  puncture  with  a  voltage  of  40,000,  or  nearly  four  times  that 
of  the  circuits  they  were  to  support. 

Porcelain  insulators  for  the  second  line  between  Niagara  Falls  and 
Buffalo,  after  the  voltage  of  transmission  had  been  raised  to  22,000, 
were  given  a  puncture  test  at  60,000  volts.  Of  these  insulators  tested 
at  60,000  volts  only  about  three  per  cent  proved  to  be  defective.  These 
puncture  tests  were  carried  out  by  placing  each  insulator  upside  down 
in  an  open  pan  containing  salt  water  to  a  depth  of  two  inches,  partly 
filling  the  pin  hole  of  the  insulator  with  salt  water,  and  then  connecting 
one  terminal  of  the  testing  circuit  with  a  rod  of  metal  in  the  pin  hole, 
and  the  other  terminal  with  the  pan.  Alternating  current  was  employed 
in  these  tests,  as  is  usually  the  case  (Volume  xviii.,  Transactions  A.  I. 
E.  E.,  pp.  514  to  520).  For  the  transmission  lines  between  Spier  Falls, 
Schenectady,  Albany,  and  Troy,  where  the  voltage  is  30,000,  the  insu- 
lators were  required  to  withstand  a  puncturing  test  with  75,000  volts 
for  a  period  of  five  minutes  after  they  had  been  soaked  in  water  for 
twenty-four  hours. 

There  is  some  difference  of  opinion  as  to  the  proper  duration  of  a 


29o    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

puncturing  test,  the  practice  in  some  cases  being  to  continue  the  test 
for  only  one  minute  on  each  insulator,  while  in  other  cases  the  time  runs 
up  to  five  minutes  or  more.  As  a  rule,  the  higher  the  testing  voltage 
compared  with  that  under  which  the  insulators  will  be  regularly  used, 
the  shorter  should  be  the  period  of  test.  Instead  of  being  tested  in  salt 
water  as  above  described,  an  insulator  may  be  screwed  onto  an  iron  pin 
of  a  size  that  fits  its  threads,  and  then  one  side  of  the  testing  circuit  put 
in  contact  with  the  pin  and  the  other  side  connected  with  the  wire  groove 
of  the  insulator.  Care  should  be  taken  where  an  iron  pin  is  used  either 
in  testing  or  for  regular  line  work,  that  the  pin  is  not  screwed  hard  up 
against  the  top  of  the  insulator,  as  this  tends  to  crack  off  the  top,  espe- 
cially when  the  pin  and  insulator  are  raised  in  temperature.  Iron  ex- 
pands at  a  much  higher  rate  than  glass  or  porcelain,  and  it  is  desirable 
to  cement  iron  pins  into  insulators  rather  than  to  screw  them  in.  There 
seems  to  be  some  reason  to  think  that  an  insulator  will  puncture  more 
readily  when  it  is  exposed  to  severe  mechanical  stress  by  the  expansion 
of  the  iron  pin  on  which  it  is  mounted. 

Tests  of  insulators  are  usually  made  with  alternating  current,  and 
the  form  of  the  voltage  curve  is  important,  especially  where  the  test  is 
made  to  determine  what  voltage  will  arc  over  the  surface  of  the  insulator 
from  the  line  wire  to  the  pin.  The  square  root  of  the  mean  square  for 
two  curves  of  alternating  voltage  or  mean  effective  voltage,  as  read  by 
a  voltmeter,  may  be  the  same  though  the  maximum  voltages  of  the  two 
curves  differ  widely.  In  tests  for  the  puncture  of  insulators,  the  average 
alternating  voltage  applied  is  more  important  than  the  maximum  volt- 
age shown  by  the  highest  points  of  the  pressure  curve,  because  of  the 
influence  of  the  time  element  with  glass  and  porcelain.  On  the  other 
hand,  when  the  test  is  to  determine  the  voltage  at  which  current  will  arc 
over  the  insulator  surface  from  the  line  wire  to  the  pin,  the  maximum 
value  of  the  pressure  curve  should  be  taken  into  consideration  because 
air  has  no  time  element,  but  permits  a  disruptive  discharge  under  a 
merely  instantaneous  voltage. 

Alternators  used  in  transmission  systems  usually  conform  approx- 
imately to  a  sine  curve  in  the  instantaneous  values  of  the  pressures  they 
develop,  and  it  is  therefore  desirable  that  tests  on  line  insulators  be  made 
with  voltages  whose  values  follow  the  sine  curve.  Either  a  single  trans- 
former or  several  transformers  in  series  may  be  employed  to  step  up  to 
the  required  voltage,  but  a  single  transformer  will  usually  give  better 
regulation  and  greater  accuracy.  An  air-gap  between  needle  points  is 
not  a  very  satisfactory  means  by  which  to  determine  the  average  voltage 


INSULATORS  FOR  TRANSMISSION  LINES.          291 

on  a  testing  circuit,  because,  as  already  pointed  out,  the  sparking  dis- 
tance between  the  needle  points  depends  mainly  on  the  maximum  instan- 
taneous values  of  the  voltage,  which  may  vary  with  the  load  on  the 
generator,  and  the  saturation  of  its  magnets.  For  accurate  results  a 
step-down  voltmeter  transformer  should  be  used  on  the  testing  circuit. 

An  insulator  that  resists  a  puncture  test  may  fail  badly  when  sub- 
jected to  a  test  as  to  the  voltage  that  will  arc  over  its  surface  from  line 
wire  to  pin.  This  arc-over  test  should  be  made  with  the  outer  surface 
of  the  insulator  both  wet  and  dry.  For  the  purpose  of  this  test  the 
insulator  should  be  screwed  onto  an  iron  pin,  or  onto  a  wooden  pin 
that  has  been  covered  with  tinfoil.  One  wire  of  the  testing  circuit 
should  then  be  secured  in  the  groove  of  the  insulator,  and  the 
other  wire  should  be  connected  to  the  iron  or  tin  foil  of  the  pin. 
The  voltage  that  will  arc  over  the  surface  of  an  insulator  from  the 
line  wire  to  the  pin  depends  on  the  conditions  of  that  surface  and  of 
the  air.  In  light  air,  such  as  is  found  at  great  elevations,  an  arc  will 
jump  a  greater  distance  than  in  dry  air  near  the  sea-level.  A  fog  in- 
creases the  distance  that  a  given  voltage  will  jump  between  a  line  wire 
and  its  insulator  pip,  and  a  heavy  rain  lengthens  the  distance  still  further. 
The  heavier  the  downpour  of  rain  the  greater  is  the  distance  over  the 
outside  surface  of  an  insulator  that  a  given  voltage  will  arc  over.  The 
angle  at  which  the  falling  water  strikes  the  insulator  surface  also  has  an 
influence  on  the  voltage  required  to  arc  over  that  surface,  a  deviation 
from  a  downpour  perpendicular  to  the  plane  of  the  lower  edge  of  the 
petticoat  of  the  insulator  seeming  to  increase  the  arcing  distance  for  a 
given  voltage. 

An  insulator  should  be  given  an  arc-over  test  under  conditions  that 
are  approximately  the  most  severe  to  be  met  in  practice.  These  condi- 
tions can  perhaps  be  fairly  represented  by  a  downpour  of  water  that 
amounts  to  a  depth  of  one  inch  in  five  minutes  for  each  square  inch  of 
the  plane  included  by  the  edge  of  the  largest  petticoat  of  the  insulator, 
when  the  direction  of  the  falling  water  makes  an  angle  of  forty-five  de- 
grees with  that  plane.  A  precipitation  of  one  inch  in  depth  on  a  horizontal 
plane  during  five  minutes  seems  to  be  a  little  greater  than  any  recorded 
by  the  United  States  Weather  Bureau.  Under  the  severe  conditions 
just  named,  the  voltage  required  to  arc  over  the  insulator  surface  from 
line  wire  to  pin  should  be  somewhat  greater  at  least  than  the  normal 
voltage  of  the  circuit  where  the  insulator  is  to  be  used.  For  the  trans- 
mission line  between  Spier  Falls  and  Schenectady,  on  which  the  maxi- 
mum voltage  is  30,000,  the  insulators  were  required  to  stand  a  test  of 


292     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

42,000  volts  when  wet,  without  arcing  over  from  line  wire  to  pin.  In 
these  wet  tests  the  water  should  be  sprayed  evenly  onto  the  insulator 
surface  like  rain,  and  the  quantity  of  water  that  strikes  the  insulator 
in  a  given  time  should  be  measured. 

When  the  outside  of  an  insulator  is  wet  with  rain,  it  is  evident  that 
most  of  the  resistance  between  the  line  wire  and  the  insulator  pin  must 
be  offered  by  the  inside  surface  of  the  petticoat  of  the  insulator.  For  this 
reason  an  insulator  that  is  to  withstand  a  very  high  voltage  so  that  no  arc 
will  be  formed  over  its  wet  outside  surface  must  have  a  wide,  dry  surface 
under  its  petticoat.  In  some  tests  of  line  insulators  reported  in  Volume 
xxi.,  Transactions  A.  I.  E.  E.,  p.  314,  the  results  show  that  the  voltage 
required  to  arc  over  from  line  wire  to  pin  depends  on  the  shortest  dis- 
tance between  them,  rather  than  on  the  distance  over  the  insulator  sur- 
face. Three  insulators,  numbered  4,  5,  and  7  in  the  trial,  were  in  each 
case  tested  by  a  gradual  increase  of  voltage  until  a  discharge  took  place 
between  the  wire  and  pin.  The  pins  were  coated  with  tinfoil,  and  the 
testing  voltage  was  applied  to  the  tie  wire  on  each  insulator  and  to  the 
tinfoil  of  its  pin.  Insulators  4,  5,  and  7  permitted  arcs  from  wire  to  pin 
when  exposed  to  73,800,  74,700,  and  74,700  volts  respectively,  the  sur- 
faces of  all  being  dry  and  clean.  The  shortest  distances  between  wires 
and  pins  over  insulator  surface  and  through  air  were  6f,  6J,  and  7$ 
inches  respectively  for  the  three  insulators,  so  that  the  arcing  voltages 
amounted  to  11,140,  11,952,  and  9,479  per  inch  of  these  distances. 
Measured  along  their  surfaces,  the  distances  between  wires  and  pins  on 
these  three  insulators  were  8,  nj,  and  15 J  inches  respectively,  so  that 
the  three  arcing  voltages,  which  were  nearly  equal,  amounted  to  9,225, 
6,640,  and  4,819  per  inch  of  these  distances.  These  figures  make  it 
plain  that  the  arcing  voltage  for  each  insulator  depends  on  the  shortest 
distance  over  its  surface  and  through  the  air,  from  wire  to  pin.  It 
might  be  expected  that  the  voltage  in  any  case  would  arc  equal  distances 
over  clean,  dry  insulator  surface  or  through  the  air,  and  the  experiments 
just  named  indicate  that  this  view  is  approximately  correct.  The  spark- 
ing distance  through  air  between  needle  points,  which  is  greater  than 
that  between  smooth  surfaces,  is  5.85  inches  with  70,000  volts,  and  7.1 
inches  with  80,000  volts  according  to  the  report  in  Volume  xix.,  A.  I. 
E.  E.,  p.  721.  Comparing  these  distances  with  the  shortest  distances 
between  wires  and  pins  in  the  tests  of  insulators  numbered  4,  5,  and  7, 
which  broke  down  at  73, 800  to  74,700  volts  when  dry,  it  seems  that  a 
given  voltage  will  arc  somewhat  further  over  clean,  dry  insulator  surface 
than  it  will  through  air.  This  view  finds  support  from  the  fact  that  only 


INSULATORS  FOR  TRANSMISSION  LINES.         293 

a  part  of  each  of  the  shortest  distances  between  wire  and  pin  was  over 
insulator  surface,  the  remainder  being  through  air  alone. 

The  fact  that  the  dry  part  of  the  surface  of  an  insulator  and  the  air 
between  its  lower  wet  edge  and  the  pin  or  cross-arm  offer  most  of  the 
resistance  between  the  line  wire  and  the  pin  and  cross-arm  is  plainly 
brought  out  by  the  results  of  the  tests  above  mentioned,  in  the  cases  of 
insulators  numbered  4  and  7.  While  73,800  volts  were  required  to  arc 
from  line-wire  to  pin  when  the  entire  insulator  was  dry  and  clean,  the 
arc  was  formed  at  only  53,400  volts  during  a  moderate  rain-storm,  in 
the  case  of  No.  4  insulator.  With  insulator  No.  7  the  arcing  voltage 
was  74,700  when  the  entire  surface  was  clean  and  dry,  but  the  arc  from 
wire  to  pin  was  started  at  52,800  volts  during  a  moderate  rain.  No.  5 
insulator  seems  to  present  an  erratic  result,  for  when  dry  and  clean  the 
arc  jumped  from  wire  to  pin  at  74,700  volts,  and  yet  during  a  moderate 
rain  no  arc  was  formed  until  a  voltage  of  70,400  was  reached.  For  each 
of  the  seven  insulators  on  which  tests  are  reported  as  above,  the  voltage 
required  to  arc  from  line  wire  to  pin  was  nearly  or  quite  as  great  during 
a  dry  snow-storm  as  when  the  insulator  surface  was  clean  and  dry. 
When  the  insulators  were  covered  with  wet  snow  their  surface  insulation 
broke  down  at  voltages  that  were  within  ten  per  cent  above  or  below  the 
arcing  voltages  during  a  moderate  rain  in  five  cases.  With  two  insulators 
the  arcing  voltages,  when  they  were  covered  with  wet  snow,  were  only 
about  sixty  per  cent  of  the  voltages  necessary  to  break  down  the  surface 
insulation  between  wire  and  pin  during  a  moderate  rain. 

When  the  outside  surface  of  an  insulator  is  wet,  as  during  a  moderate 
rain,  it  seems  that  the  under  surface  of  the  insulator,  and  the  distance 
through  air  from  the  lower  wet  edge  of  the  insulator  to  the  pin  or  cross- 
arm,  make  up  most  of  the  insulation  that  prevents  arcing  over  from  the 
wire  to  the  pin  or  cross-arm.  It  further  appears  that  it  is  useless  to 
extend  the  distance  across  the  dry  under  surface  of  the  insulator  indefi- 
nitely without  a  corresponding  increase  of  the  direct  distance  through  air 
from  the  lower  wet  edge  of  the  insulator  to  the  wood  of  cross-arm  or  pin. 
Insulator  No.  7  in  the  tests  under  consideration  had  a  diameter  at  the 
lower  edge  of  its  outer  petticoat  of  seven  inches,  and  was  mounted  on  a 
standard  wooden  pin.  The  diameter  of  this  pin  in  the  plane  of  the  lower 
edge  of  the  insulator  was  probably  about  ij  inches,  so  that  the  radial 
distance  through  air  from  this  edge  to  the  pin  must  have  been  2j  inches 
approximately.  During  a  moderate  rain  the  surface  insulation  of  this 
insulator  broke  down  and  an  arc  was  formed  from  wire  to  pin  with  52,800 
volts.  The  sparking  distance  between  needle  points  at  50,000  volts  is 


294    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

3.55  inches,  according  to  Volume  xix.,  A.  I.  E.  E.,  p.  721,  and  must 
be  shorter  between  smooth  surfaces,  such  as  the  wire  and  pin  in  question, 
so  that  nearly  all  of  the  52,800  volts  in  this  case  must  have  been  required 
to  jump  the  2f  inches  of  air,  leaving  very  little  to  overcome  the  slight 
resistance  of  the  wet  outside  surface  of  the  insulator.  On  this  insulator 
the  surface  distance  from  wire  to  pin  was  15^  inches,  while  the  shortest 
breaking  distance  was  only  yf  inches,  so  that  the  distance  across  the  dry 
under  surface  of  the  insulator  must  have  been  15^  —  (yf  —  2f)  =  loj 
inches  approximately.  It  is  evidently  futile  to  put  a  path  ioj  inches 
long  across  dry  insulator  surface  in  parallel  with  a  path  only  2f  inches 
long  in  air,  as  an  arc  will  certainly  jump  this  shorter  path  long  before 
one  will  be  formed  over  the  longer.  The  same  line  of  reasoning  applies 
to  No.  3  insulator  in  this  test,  which  had  a  diameter  of  6}  inches,  a  surface 
distance  from  wire  to  pin  of  13  inches,  and  a  minimum  distance  of  yj 
inches,  and  whose  surface  insulation  broke  down  at  48,600  volts  during 
a  moderate  rain.  The  necessity  of  increasing  the  distance  between  the 

INSULATORS  ON  TRANSMISSION  LINES. 


Location  of  Line. 

Voltage 
of 
Line. 

Material 
of 
Insulator. 

Inches 
Diameter 
of 
Insulator. 

Inches 
Height 
of 
Insulator. 

Electra  to  San  Francisco  

60,000 
60,000 
50,000 
50,000 
40,000 
33,000 
30,000 
25,000 
25,000 

22,000 
I3,OOO 
I2,OOO 

Porcelain 
Porcelain 
Glass 
Porcelain 
Glass 
Porcelain 
Porcelain 
Glass 
Porcelain 
Porcelain 
Porcelain 
Glass 

II 
II 
9 

10 

I* 

8j 

ij 

51 

5 

«i 

nl 

12 

i3j 

5J 

41 
61 

ii 
l\ 

4^ 

1 

Colgate  to  Oakland 

Canon  Ferry  to  Butte 

Shawinigan  Falls  to  ^Montreal  .  . 

Provo  around  Utah  Lake  . 

Santa  Ana  River  to  Los  Angeles.  .  .  . 
Spier  Falls  to  Schenectady  

Apple  River  Falls  to  St  Paul  

Charnbly  to  Montreal 

Niagara  Falls  to  Buffalo 

Portsmouth  to  Pelham,  N.  H  

Garvins  Falls  to  Manchester,  N.  H. 

lower  wet  edges  of  insulators  and  the  pins  and  cross-arm,  as  well  as  the 
distance  across  the  dry  under  surfaces  of  insulators,  led  to  the  adoption 
of  the  so-called  umbrella  type  for  some  high-voltage  lines.  In  this  type 
of  insulator  the  main  or  outer  petticoat  is  given  a  relatively  great  diam- 
eter, and  instead  of  being  bell-shaped  is  only  moderately  concave  on  its 
under  side.  With  an  insulator  of  this  type  mounted  on  a  large,  long  pin, 
the  lower  edge  of  the  umbrella-like  petticoat  may  be  far  removed  from 
the  pin  and  cross-arm.  Beneath  the  large  petticoat  of  such  insulators 
for  high  voltages  there  are  usually  one  or  more  smaller  petticoats  or 


INSULATORS  FOR  TRANSMISSION  LINES. 


295 


sleeves  that  run  down  the  pin,  and  increase  the  distance  between  it  and 
the  lower  edge  of  the  largest  petticoat. 

The  inner  petticoat  or  sleeve  that  runs  down  over  the  pin  and  some- 
times reaches  nearly  to  the  cross-arm,  of  course  becomes  wet  on  its 
outside  surface  and  at  its  lower  edge  during  a  rain;  but  between  this 
lower  wet  part  of  the  inner  petticoat,  or  sleeve,  and  the  lower  wet  edge 
of  the  larger  outside  petticoat,  there  is  a  wide,  dry  strip  of  insulator  sur- 
face. A  result  is  that  an  arc  over  the  surface  of  the  outside  petticoat 
can  reach  the  wet  edge  of  the  sleeve  only  by  crossing  the  strip  of  dry 
under  surface  or  jumping  through  the  air. 

The  same  type  of  insulator  is  used  on  the  6o,ooo-volt  lines  between 
Electra  and  San  Francisco  and  between  Colgate  and  Oakland,  each 
insulator  having  an  outer  petticoat  1 1  inches  in  diameter  and  one  inner 
petticoat  or  sleeve  6 J  inches  in  diameter.  This  inner  petticoat  runs  down 
the  pin  for  a  distance  of  7^  inches  below  the  outer  petticoat.  Slightly 

INSULATORS  ON  TRANSMISSION  LINES. 


Location  of  Line. 

Inches  from 
Top  of  In- 
sulator to 
Cross-arm. 

Inches  from 
Outside 
Petticoat  to 
Cross-arm. 

Inches  from 
Lowest 
Petticoat  to 
Cross-arm. 

c^o>        1 

C  3  M-*-1  ^J 
^  O  _O  O  -^ 

Electra  to  San  Francisco 

He*  Hdi-tiiiidaoKfci  HM 
Tt  10  rO\O  00  O  O  00 

II 
Pj 

7\ 

7i 

5i 

1 

si 

4 

1 

4i 

3 

2 

8i 

0 

3f 

2$ 

Colgate  to  Oakland  . 

Canon  Ferry  to  Butte  .  . 

Shawinigan  Falls  to  Montreal  .  . 

Santa  Ana  River  to  Los  Angeles.  .  . 
Spier  Falls  to  Schenectady  

Niagara  Falls  to  Buffalo  

Chambly  to  ^Montreal 

On  each  of  the  lines  named  in  this  table  the  wires  are  strung  on  the  tops  of 
their  insulators. 

different  pins  are  used  for  mounting  the  insulators  on  the  two  transmis- 
sion lines  just  named,  so  that  on  the  former  the  distance  through  air 
from  the  lower  edge  of  the  outer  petticoat  to  the  cross-arm  is  1 1  inches, 
and  on  the  latter  the  corresponding  distance  is  1 1  \  inches.  On  the  Elec- 
tra line  the  lower  edge  of  the  inner  petticoat  of  each  insulator  is  about 
3i  inches,  and  on  the  Colgate  line  about  4  inches  above  the  cross-arm. 
The  Canon  Ferry  line  is  carried  on  insulators  each  of  which  has  three 
short  petticoats  and  a  long  separate  sleeve  that  runs  down  over  the  pin 
to  within  i£  inches  of  the  cross-arm.  This  sleeve  makes  contact  with 
its  insulator  near  the  pin  hole.  The  outside  petticoat  of  each  insulator 


296    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

on  this  line  is  7}  inches  above  the  cross-arm  and  6J  inches  above  the 
lower  end  of  the  sleeve.  Both  the  main  insulator  and  the  sleeve,  in 
this  case,  are  of  glass. 

White  porcelain  insulators  are  used  to  support  the  5o,ooo-volt  Sha- 
winigan  line,  and  are  of  a  recent  design.  Each  of  these  insulators  has 
three  petticoats  ranged  about  a  central  stem  so  that  their  lower  edges 
are  4^  inches,  9  inches,  and  13  inches  respectively,  below  the  top.  The 
highest  petticoat  is  10  inches,  the  intermediate  9!  inches,  and  the  lowest 
4j  inches  in  diameter.  The  height  of  this  insulator  is  13  inches,  com- 
pared with  ii J  inches  for  those  used  on  the  Electra  and  Colgate  lines 
and  12  inches  for  the  combined  insulator  and  sleeve  used  on  the  Canon 
Ferry  line.  When  mounted  on  its  pin,  this  insulator  on  the  Shawinigan 
line  holds  its  wire  i6j  inches  above  the  cross-arm,  compared  with  a  cor- 
responding distance  of  14^  inches  on  the  Electra,  15  inches  on  the  Col- 
gate, and  13  J  inches  on  the  Canon  Ferry  line.  The  two  upper  petticoats 
on  each  of  these  insulators  are  much  less  concave  than  the  lowest  one, 
and  the  edges  of  all  three  stand  respectively  nj,  7},  and  3^  inches  above 
the  cross-arm.  From  the  edge  of  the  top  to  the  edge  of  the  bottom 
petticoat  the  direct  distance  is  8J  inches. 

Of  the  three  transmission  lines  above  named  that  operate  at  50,000 
to  60,000  volts,  that  between  Shawinigan  Falls  and  Montreal  leads 
as  to  distances  between  the  line  wire  and  insulator  petticoats  and  the 
cross-arm.  On  the  Santa  Ana  line,  where  the  voltage  is  33,000,  the 
insulator  is  of  a  more  ordinary  type,  being  of  porcelain,  6J  inches  in 
diameter,  4^  inches  high,  and  having  the  lower  edges  of  its  three  petti- 
coats in  the  same  plane.  Each  of  these  insulators  holds  its  wire  8f 
inches  above  the  cross-arm,  and  has  all  of  its  petticoats  3^  inches  above 
the  cross-arm.  Unlike  the  three  insulators  just  described,  which  are 
mounted  on  wooden  pins,  this  Santa  Ana  insulator  has  a  pin  with  an 
iron  core,  wooden  threads,  and  porcelain  base.  This  base  extends  up 
from  the  cross-arm  a  distance  of  3 \  inches,  and  the  wooden  -sleeve,  in 
which  the  threads  for  the  insulator  are  cut,  runs  down  over  the  central 
bolt  of  the  pin  to  the  top  of  the  porcelain  base,  which  is  f-inch  below 
the  petticoats. 

The  30,000- volt  lines  from  Spier  Falls  are  carried  10}  inches  above 
their  cross-arms  by  triple  petticoat  porcelain  insulators.  Each  of  these 
insulators  is  8J  inches  in  diameter,  6f  inches  high,  and  is  built  up  of 
three  parts  cemented  together.  A  malleable-iron  pin  cemented  into  each 
insulator  with  pure  Portland  cement  carries  the  outside  petticoat  7^ 
inches  and  its  lowest  petticoat  4^  inches  above  the  cross-arm.  When 


INSULATORS  FOR  TRANSMISSION  LINES.          297 

the  voltage  on  the  Spier  Falls  lines  was  raised  from  about  13,000  to 
30,000,  the  circuits  being  carried  in  part  by  one-piece  porcelain  in- 
sulators, a  number  of  these  insulators  were  punctured  at  the  higher 
pressures,  and  some  cross-arms  and  poles  were  burned  as  a  result.  No 
failures  resulted  on  those  parts  of  these  lines  where  the  three-part  insula- 
tors were  in  use.  The  second  pole  line  between  Niagara  Falls  and 


FIG.  93A.— The  Old  and  New  Insulators  on  the  Niagara  Falls-Buffalo  Line, 

Buffalo  was  designed  to  carry  circuits  at  22,000  volts,  or  twice  that  for 
which  the  first  line  was  built.  Porcelain  insulators  were  employed  on 
both  of  these  lines,  but  while  the  n,ooo-volt  line  was  carried  on  three- 
petticoat  insulators,  each  with  a  diameter  of  7  inches  and  a  height  of  5^ 
inches,  the  2 2,000- volt  line  was  mounted  on  insulators  each  7^  inches  in 
diameter  and  7  inches  high,  with  only  two  petticoats.  The  older  insula- 
tor has  its  petticoats  2  inches  above  the  cross-arm,  and  the  lower  petti- 
coat of  the  new  insulator  is  3  inches  above  the  arm.  These  two  insulators 
illustrate  the  tendency  to  lengthen  out  along  the  insulator  axis  as  the 
voltage  of  the  circuits  to  be  carried  increases. 

For  future  work  at  still  higher  voltages,  the  advantage  as  to  both  first 
cost  and  insulating  qualities  seems  to  lie  with  insulators  that  are  very 
long  in  an  axial  direction,  and  which  have  their  petticoats  arranged  one 
below  the  other  and  all  of  about  the  same  diameter,  rather  than  with 
insulators  of  the  umbrella  type,  like  those  on  the  Electra  and  Colgate 
lines. 


CHAPTER  XXII. 

DESIGN  OF  INSULATOR  PINS  FOR  TRANSMISSION  LINES. 

BENDING  strains  due  to  the  weights,  degree  of  tension,  and  the  direc- 
tions of  line  wires,  plus  those  resulting  from  wind-pressure,  are  the  chief 
causes  that  lead  to  the  mechanical  failure  of  insulator  pins. 

Considering  the  unbalanced  component  of  these  forces  at  right 
angles  to  the  axis  of  the  pin,  which  alone  produce  bending,  each  pin  may 
be  considered  as  a  beam  of  circular  cross  section  secured  at  one  end  and 
loaded  at  the  other. 

For  this  purpose  the  secured  end  of  the  beam  is  to  be  taken  as  the 
point  where  the  pin  enters  its  cross-arm,  and  the  loaded  end  of  the  beam 
is  the  point  where  the  line  wire  is  attached  to  the  insulator.  The  dis- 
tance between  these  two  points  is  the  length  of  the  beam.  The  maxi- 
mum strain  in  the  outside  fibres  of  a  pin  measured  in  pounds  per  square 
inch  of  its  cross  section,  represented  by  S,  may  be  found  from  the  for- 
mula, 

PX 

"  .0982  D3 

where  P  is  the  pull  of  the  wire  in  pounds,  D  is  the  diameter  of  the  pin 
at  any  point,  and  X  is  the  distance  in  inches  of  that  point  from  the  wire. 
Inspection  of  this  formula  shows  that  S,  the  maximum  strain  at  any  point 
in  the  fibres  of  a  pin,  when  the  pull  of  the  line-wire,  P,  is  constant,  in- 
creases directly  with  the  distance,  X,  from  the  wire  to  the  point  where 
the  strain,  S,  takes  place.  This  strain,  S,  with  a  constant  pull  of  the 
line  wire,  decreases  as  the  cube  of  the  diameter,  D,  at  the  point  on  the 
pin  where  S  occurs  increases.  That  cross  section  of  a  pin  just  at  the 
top  of  its  hole  in  the  cross-arm  is  thus  subject  to  the  greatest  strain,  if 
the  pin  is  of  uniform  diameter,  because  this  cross  section  is  more  distant 
from  the  line  wire  than  any  other  that  is  exposed  to  the  bending  strain. 
For  this  reason  it  is  not  necessary  to  give  a  pin  a  uniform  diametei 
above  its  cross-arm,  and  in  practice  it  is  always  tapered  toward  its  top. 
Notwithstanding  this  taper,  the  weakest  point  in  pins  as  usually  made 
is  just  at  the  top  of  the  cross-arm,  and  it  is  at  this  cross  section  where 
pins  usually  break.  This  break  comes  just  below  the  shoulder  that  is 

2Q8 


DESIGN  OF  INSULATOR  PINS.  299 

turned  on  each  pin  to  prevent  its  slipping  down  through  the  hole  in  its 
cross-arm.  If  the  shoulder  on  a  pin  made  a  tight  fit  all  around  down 
onto  the  cross-arm,  the  strength  of  the  pin  to  resist  bending  would  be 
thereby  increased,  but  it  is  hard  to  be  sure  of  making  such  fits,  and  they 
should  not  be  relied  on  to  increase  the  strength  of  pins.  By  giving  a 
pin  a  suitable  taper  from  its  shoulder  at  the  cross-arm  to"  its  top,  the 
strain  per  square  inch,  S,  in  the  outside  fibres  of  the  pin  may  be  made 
constant  for  every  cross  section  throughout  its  length  above  the  cross- 
arm,  whatever  that  length  may  be.  The  formula  above  given  may  be 
used  to  determine  the  diameters  of  a  pin  at  various  cross  sections  that 
will  make  the  maximum  stress,  S,  at  each  of  these  cross  sections  con- 
stant. By  transposition  the  formula  becomes 

P 

D3  =  -      —  z-  X. 
.0982  S 

Where  the  pin  is  tapered  so  that  S  is  constant  for  all  cross  sections,  then 

•p 

for  any  pull,  P,  of  the  line  wire  on  the  pin  the  quantity  (  —  -  —  -  j    must 

be  constant  at  every  diameter,  D,  distant  any  number  of  inches,  X, 

(      P      \ 

from  the  point  where  the  wire  is  attached.     If  the  constant,  (  -  —} 

^.0982  S/ 

is  found  for  any  one  cross  section  of  a  pin,  therefore,  the  diameter  at 
each  other  cross  section  with  the  same  maximum  stress,  S,  may  be 
readily  found  by  substituting  the  value  of  this  constant  in  the  formula. 
The  so-called  "standard''  wooden  pin  that  has  been  very  generally  used 
for  ordinary  distribution  lines,  and  to  some  extent  even  on  high-voltage 
transmission  lines,  has  a  diameter  of  nearly  1.5  inches  just  below  the 
shoulder.  The  distance  of  the  line  wire  above  this  shoulder  varies  be- 
tween about  4.5  and  6  inches,  according  to  the  type  of  insulator  used, 
and  to  whether  the  wire  is  tied  at  the  side  or  top  of  the  insulator.  If  the 
line  wire  is  tied  to  the  insulator  5  inches  above  the  shoulder  of  one  of  the 
standard  pins,  then  X  becomes  5,  and  D  becomes  1.5  in  the  formula 
last  given.  From  that  formula  by  transposition  and  substitution 
P  D3  (i-5)3 


p 

Substituting  0.675  for  tne  quantity  -  -   in    the   formula    D3  = 

0.0982  S 

-  X  gives  the  formula  D3  =  0.675  X,  from  which  the  diame- 

0.0982  b 

ters  at  all  cross  sections  of  a  tapered  pin  above  its  shoulder,  that  will 


300    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


give  it  a  strength  just -equal  to  that  of  a  section  of  1.5  inches  diameter 
and  5  inches  from  the  line  wire,  may  be  found.  To  use  the  formula 
for  this  purpose  it  is  only  necessary  to  substitute  any  desired  values  of 
X  therein  and  then  solve  in  each  case  for  the  corresponding  values  of  D. 
Let  it  be  required,  for  instance,  to  determine  what  diameter  a  pin  should 
have  at  a  cross  section  one  inch  below  the  line  wire  in  order  that  the 
maximum  strain  at  that  cross  section  may  equal  the  corresponding  strain 
at  a  cross  section  five  inches  below  the  line  wire  and  of  i  .5  inch  diameter. 
Substituting  one  as  the  value  of  X,  the  last-named  formula  becomes 
D3  =  0.675,  and  from  this,  D  =  0.877,  which  shows  that  the  diameter 
of  the  pin  one  inch  below  the  line  wrire  should  be  0.87 7-inch.  A  similar 
calculation  will  show  that  if  a  pin  is  long  enough  so  that  a  cross  section 
above  the  cross-arm  is  1 2  inches  below  the  line  wire,  the  diameter  of  this 
cross  section  should  be  equal  to  the  cube  root  of  0.675  *  1 2  —  8- I  >  which 
is  2.008,  or  practically  two  inches.  It  should  be  observed  that  the  calcu- 
lations just  made  have  nothing  to  do  with  the  ability  of  a  pin  to  resist 
any  particular  pull  of  its  line  wire.  These  calculations  simply  show 
what  diame'ters  a  pin  should  have  at  different  distances  below  its  line 
wire  in  order  that  the  maximum  stress  at  each  of  its  cross  sections  may 
equal  that  at  a  cross  section  5  inches  below  the  wire  where  the  diameter 
is  1.5  inches.  In  Vol.  xx.,  A.  I.  E.  E.,  pp.  415  to  419,  specifications 
are  proposed  for  standard  insulator  pins  based  on  calculations  like 
those  just  made.  As  a  result  of  such  calculations,  the  following  table 
for  the  corresponding  values  of  X  and  D,  as  used  in  the  above  formula, 
are  there  presented,  each  expressed  in  inches. 


X          D 

X          D 

X          D 

X           D 

i         0.877 

<r          I.<OO 

0         I  82=; 

I  c           217 

2       .  1.106 

6.       1.^02 

10  .      1.888 

17           22^ 

•?.       .  .  1.  263 

7.       .  1.678 

II  ..     .  .  I.Qs 

10           2  34. 

4-  •      .  -  1  .30^ 

8..      ..  I.7S4 

13  2.06 

21  2  42 

A  pin  twenty-one  inches  long  between  the  line  wire  and  the  cross- 
arm  will  have  a  uniform  strength  to  resist  the  pull  of  the  wire  if  it  has 
the  diameter  given  in  this  table  at  the  corresponding  distances  below 
the  line  wire.  From  this  it  follows  that  a  pin  of  any  length  between 
wire  and  cross-arm  corresponding  to  X  in  the  table  will  be  equally 
strong  to  resist  a  pull  of  the  line  wire  as  a  standard  1.5 -inch  diameter  pin 
with  its  wire  five  inches  above  the  cross-arm.  In  other  words,  if  a  pin 
that  is  twenty-one  inches  long  between  the  line  wire  and  the  cross-arm 


DESIGN  OF  INSULATOR  PINS. 


has  the  diameters  given  in  the  table  at  the  corresponding  distances  below 
the  wire,  then  a  pin  of  equal  strength  to  resist  bending,  and  of  any 
shorter  length,  would  correspond  in  the  part  above  the  cross-arm  to  an 
equal  length  cut  from  the  top  end  of  the  longer  pin.  Designating  that 
part  of  a  pin  that  is  above  the  cross-arm  as  the  "stem,"  and  that  part 
in  the  cross-arm  as  the  "shank,"  each  pin  in  the  specifications  under 
consideration  is  named  by  the  length  of  its  stem,  as  a  5-,  7-  or  n-inch 
pin.  It  is  proposed  that  each  pin  of  whatever  length  be  threaded  for  a 
distance  of  2.5  inches  at  the  top  of  its  stem  with  four  threads  per  inch, 
the  sides  of  each  thread  being  at  an  angle  of  ninety  degrees  with  each 
other.  Each  thread  is  to  cut  into  the  pin  about  ^\  inch,  come  to  a 
sharp  angle  at  the  bottom,  and  be  about  TV  inch  wide  on  top.  At  the 
end  of  the  pin  the  proposed  diameter  over  the  thread  is  one  inch  in  all 
cases,  and  at  the  lower  end  of  the  threaded  portion  the  outside  diam- 
eter is  1.25  inches.  Near  the  end  of  the  pin  the  diameter  at  the  bot- 
tom of  the  thread  is  thus  only  Tf  inch,  and  the  corresponding  diameter 
at  the  lower  end  of  the  threaded  portion  is  about  iy^  inches  on  all  pins. 
Each  pin  is  to  have  a  square  shoulder  to  rest  on  the  cross-arm,  and  the 
diameter  of  this  shoulder  is  to  be  J  inch  greater  than  the  nominal  diameter 
of  the  shank  of  the  pin.  The  proposed  length  of  this  shoulder  on  all  pins 
is  J  inch  before  the  taper  begins.  The  actual  diameter  of  the  shank  of 
each  pin  just  below  its  shoulder  is  to  be  -fa  inch  less  than  the  nominal 
diameter,  and  the  actual  diameter  of  the  lower  end  of  each  shank  is  to 
be  y*j-  inch  less  than  the  nominal  diameter.  With  these  explanations 
the  proposed  sizes  of  pins  have  dimensions  as  follows  in  inches : 


Length  of 
Stem. 

Length  of 
Shlnk. 

Nominal 
Diameter  of 
Shank. 

Length  of 
Stem. 

Length  of 
Shank. 

Nominal 
Diameter  of 
Shank. 

5 

4i 

i£ 

13 

4J 

2j 

7 

4\ 

if 

15 

4i 

21 

9 

4' 

JI 

17 

5* 

*i 

ii 

4^ 

2 

19 

si 

a* 

In  order  rightly  to  appreciate  the  utility  of  this  table  of  proposed 
standard  pins,  it  is  necessary  to  have  in  mind  the  fact  that  all  the  dimen- 
sions are  based  on  the  assumption  that  a  wooden  pin  with  a  shank  of 
one  and  one-half  inches  diameter,  and  with  its  line  wire  attached  five 
inches  above  the  cross-arm,  is  strong  enough  for  general  use  on  trans- 
mission lines.  Such  an  assumption  covers  a  wide  range  of  practice,  but 
its  truth  may  well  be  doubted  for  many  cases.  That  this  assumption 


3o2     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

does  form  the  basis  of  the  entire  table  is  clearly  shown  by  the  fact  that 
the  calculated  diameter  at  the  shank  of  each  pin  is  made  to  depend  on 
a  uniform  pull,  P,  of  the  line  wire,  giving  a  uniform  maximum  stress,  S,  in 
the  outer  fibres  of  the  wood  just  where  the  shank  joins  the  stem.  In  other 
words,  every  pin  in  the  table  is  designed  to  break  with  a  uniform  pull  of 
the  line  wire,  provided  that  the  point  on  the  insulator  where  the  wire  is 
attached  is  just  on  a  level  with  the  top  of  its  pin  in  each  case.  It  will 
at  once  occur  to  practical  men  that  while  a  five-inch  pin  with  one  and 
one-half  inch  shank,  or  a  larger  pin  of  equal  ability  to  resist  the  pull  of 
a  line  wire,  may  be  strong  enough  for  the  conductors  of  some  transmis- 
sion lines,  this  same  pin  may  be  entirely  too  weak  for  the  longer  spans, 
sharper  angles,  and  heavier  conductors  of  other  lines. 

Thus,  on  the  sixty-five-mile  line  between  Canon  Ferry  and  Butte, 
Mont.,  each  conductor  is  of  copper  and  has  a  cross  section  of  106,500 
cm.,  while  on  the  older  line  between  Niagara  Falls  and  Buffalo  each 
copper  conductor  has  a  cross  section  of  350,000  cm.  Evidently  with 
equal  conditions  as  to  length  of  span,  amount  of  sag,  and  sharpness  of 
angles  on  these  two  lines,  pins  ample  in  strength  for  the  smaller  wire 
might  be  much  too  weak  for  the  larger  wire. 

A  little  consideration  will  show  that  it  is  neither  rational  nor  desir- 
able to  adopt  pins  of  uniform  strength  for  all  transmission  lines,  but  that 
several  degrees  of  strength  are  necessary  to  correspond  with  the  range 
in  sizes  of  conductors  in  regular  use.  The  size  of  pins  for  use  on  any 
transmission  line,  when  the  maximum  bending  strain  exerted  by  the 
conductors  has  been  determined,  should  be  found  by  calculation  and 
experiment,  or  by  experiment  alone.  According  to  Trautwine,  the 
average  compressive  strength  of  yellow  locust  is  9,800  pounds,  of  hickory 
8,000  pounds,  and  of  white  oak  7,000  pounds  per  square  inch  in  the  direc- 
tion of  the  grain.  These  compressive  strengths  are  less  than  the  tensile 
strengths  of  the  same  woods,  and  should  therefore  be  employed  in  calcu- 
lation, since  the  fibres  on  one  side  of  a  bending  pin  are  compressed  while 
the  fibres  on  the  other  side  are  elongated.  Substituting  1,000  for  the 

P  X 

value  of  S  in  the  formula,  S  —  -          — ,  and  also  5  for  the  value  of 

.0982  D3 

X,  and  ij  for  the  value  of  D,  the  resulting  value  of  P  is  found  to  be 
736.5  pounds.  This  result  shows  that  with  a  locust  pin  of  ij  inches 
diameter  at  the  shank,  and  with  its  line  wire  attached  five  inches  above 
the  shoulder,  the  unbalanced  side  pull  of  the  wire  that  will  break  the 
pin  by  bending  is  736  pounds,  provided  that  the  wood  of  the  pin  has  a 
strength  of  i  ,000  pounds  per  square  inch  in  compression.  As  all  of  the 


DESIGN  OF  INSULATOR  PINS.  303 

proposed  standard  pins  in  the  above  table  are  designed  for  uniform 
strength  to  resist  the  same  pull  of  a  line  wire  attached  on  a  level  with 
the  top  of  the  pin  in  each  case,  it  follows  that  the  pull  of  736  pounds  by 
the  wire  will  break  any  one  of  these  pins  under  the  conditions  stated. 

The  calculation  just  made  takes  no  account  of  the  fact  that  the  actual 
diameter  of  the  shank  of  each  pin  just  below  the  shoulder  is  ^  inch  less 
than  the  nominal  diameter,  but  this  of  course  reduces  the  strength  some- 
what. Trautwine  states  that  the  figures  above  given  for  the  compressive 
strengths  of  wood  are  only  averages  and  are  subject  to  much  variation. 
Of  course  no  pin  should  be  knowingly  loaded  in  regular  practice  to  the 
breaking  point,  and  to  provide  against  variations  in  the  strength  of  wood, 
and  for  unexpected  strains,  a  liberal  factor  of  safety,  say  four,  should  be 
adopted  in  fixing  the  maximum  strains  on  insulator  pins.  Applying  this 
factor  to  the  calculations  just  made,  it  appears  that  the  maximum  pull 
of  the  line  wire  at  the  top  of  any  one  of  the  above  proposed  standard 
pins  should  not  exceed  736  -r-  4  =  184  pounds  in  regular  work.  A 
little  calculation  will  readily  show  that  the  side  pull  of  some  of  the  larger 
conductors  now  in  use  on  transmission  lines  will  greatly  exceed  184 
pounds  under  conditions,  as  to  sag,  angles  and  wind  pressure,  that  are 
frequently  met  in  practice. 

On  page  448,  Vol.  xx.,  A.  I.  E.  E.,  some  tests  are  reported  on  six 
locust  wood  pins  with  shank  diameters  of  IT\  to  ii  inches.  Each  of 
these  pins  was  tested  by  inserting  its  shank  in  a  hole  of  ij  inches  diam- 
eter in  a  block  of  hard  wood,  and  then  applying  a  strain  at  about  right 
angles  to  the  pin  and  about  4^  inches  from  the  block  by  means  of  a 
Seller's  machine.  The  pull  on  each  pin  was  applied  gradually,  and  in 
most  of  the  pins  the  fibres  of  the  wood  began  to  part  when  the  side  pull 
reached  700  to  750  pounds,  though  the  maximum  loads  sustained  were 
about  ten  per  cent  above  these  figures.  The  average  calculated  value 
of  S,  the  compressive  strength  of  the  wood  in  these  pins,  was  11,130 
pounds  per  square  inch  on  the  basis  of  the  loads  at  which  the  fibres  of 
the  wood  began  to  break,  and  13,623  pounds  per  square  inch  for  the 
loads  at  which  the  pins  gave  way.  On  pages  650  to  653  of  the  volume 
last  cited,  results  are  reported  of  tests  on  twenty-two  pins  of  eucalyptus 
wood,  which  is  generally  used  for  this  purpose  in  California.  Twelve 
of  these  pins  were  of  a  size  much  used  in  California  on  lines  where  the 
voltage  is  not  above  30,000.  Each  of  the  twelve  pins  was  6j  inches 
long  in  the  stem,  4$  inches  long  in  the  shank,  i  J  inches  in  diameter  at 
the  shank,  2  inches  in  diameter  at  the  square  shoulder  where  the  shank 
joins  the  stem,  and  if  inches  in  diameter  at  the  top  of  the  thread.  The 


3o4    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

pins  were  tested  by  mounting  each  of  them  in  a  cross-arm,  securing  the 
cross-arm  in  a  testing  machine  so  that  the  pin  was  horizontal,  placing 
an  insulator  on  the  pin,  and  exerting  the  strain  on  a  cable  wrapped 
around  the  side  groove  of  the  insulator.  This  cable  varied  a  little  from 
right  angles  to  the  axis  of  each  pin,  but  the  component  of  the  strain  at 
right  angles  to  this  axis  was  calculated  and  the  breaking  load  here  men- 
tioned is  that  component.  Nearly  all  of  these  twelve  pins  broke  square 
off  at  the  cross-arm. 

For  a  single  pin,  the  lowest  breaking  strain  was  705  pounds,  the 
largest  1,360  pounds,  and  the  average  for  the  twelve  pins  was  1,085 
pounds.  Unfortunately,  the  exact  distance  of  the  cable  from  the  cross- 
arm  is  not  stated,  but  as  the  cable  was  wound  about  the  side  groove  of 
the  insulator  it  was  probably  either  in  line  with  or  a  little  below  the  top 
of  the  pin.  It  seems  probable  also  that  the  diameter  of  these  pins  at  the 
shoulder — that  is,  two  inches — may  have  increased  the  breaking  strain 
somewhat  by  giving  the  shoulder  a  good  bearing  on  the  cross-arm.  The 
ten  other  pins  were  of  the  size  in  use  on  the  6o,ooo-volt  line  between 
Colgate  power-house  and  Oakland,  Cal.  Each  of  these  pins  had  a 
length  of  5 f  inches  and  a  maximum  diameter  of  2j  inches  in  the  shank, 
and  a  length  of  lof  inches  in  the  stem,  with  a  diameter  of  2^  inches  at 
the  shoulder.  This  shoulder  was  not  square,  but  its  surface  formed  an 
angle  of  forty-five  degrees  with  the  axis  of  the  pin,  and  this  bevel  shoulder 
took  up  J  inch  of  the  length  just  given  for  the  stem  of  the  pin.  At  2\ 
inches  from  its  threaded  end  the  stem  of  the  pin  had  a  diameter  of  i-f-f 
inches,  and  the  diameter  slopes  to  if  inches  at  two  inches  from  the  end. 
The  two  inches  of  length  at  the  top  of  the  stem  has  the  uniform  diameter 
of  if  inches,  and  is  threaded  with  four  threads  per  inch  for  the  insulator. 
Each  of  these  ten  pins  was  tested,  as  already  described,  until  it  broke, 
but  the  break  in  this  case  started  as  a  split  at  the  lower  end  of  the  threaded 
portion  and  ran  down  the  stem  to  the  shoulder  in  a  line  nearly  parallel 
with  the  axis  of  the  pin.  The  pull  on  the  cable  at  right  angles  to  the 
axis  of  each  pin  had  a  maximum  value  of  1,475  pounds  in  one  case,  and 
a  corresponding  value  of  3,190  pounds  in  another,  while  the  average 
breaking  strain  for  the  ten  pins  was  2, 310  pounds.  Unfortunately,  the 
report  of  this  test  above  named  does  not  distinctly  state  just  how  far  the 
testing  cable  was  attached  above  the  shank  of  each  of  these  large  pins; 
but  it  seems  probable  that  the  same  insulator  was  used  with  the  larger 
as  with  the  smaller  pins,  and  if  this  was  so  the  testing  cable  was  attached 
near  the  end  of  each  pin,  as  this  cable  was  wound  about  the  side  groove 
of  the  insulator  used  on  the  smaller  pins.  With  the  types  of  insulator 


DESIGN  OF  INSULATOR  PINS.  305 

in  actual  use  on  the  Colgate  and  Oakland  line  the  wire  is  carried  at  the 
top  groove  and  its  centre  is  about  two  and  a  half  inches  above  the  top 
of  the  pin.  It  is  therefore  probable  that  these  pins  would  not  withstand 
as  great  strains  on  the  lines  as  they  did  in  these  tests.  The  bevel  shoulder 
on  each  of  these  larger  pins  no  doubt  increases  its  ability  to  resist  a  bend- 
ing strain,  because  the  bevel  surface  fits  tightly  down  into  a  counterbore 
in  the  cross-arm.  Where  the  pin  has  a  shoulder  at  right  angles  with  the 
axis,  as  is  more  usually  the  case,  and  the  top  of  the  cross-arm  is  a  little 
rounding,  the  square  shoulder  does  not  have  a  firm  seat  and  is  of  slight 
importance  as  far  as  the  strength  of  the  pin  to  resist  a  bending  strain  is 
concerned.  Evidently  the  weakest  point  in  the  ten  larger  pins  of  this 
test  was  at  the  lower  end  of  the  threaded  portion,  since  in  each  case  the 
break  was  in  the  form  of  a  long  split  starting  where  the  thread  ended. 
There  seems  to  be  no  sufficient  reason  for  the  reduction  of  the  diameter 
of  a  pin  intended  for  a  heavy  line  wire  to  a  diameter  as  small  as  one 
inch  at  the  threaded  end,  or  for  limiting  the  length  of  the  threaded  por- 
tion to  2.5  inches,  as  proposed  in  the  specifications  for  standard  pins. 
It  is  certain  that  the  cost  of  the  pin  would  be  no  more  if  its  diameter  at 
the  threaded  end  were  i  J  or  i  f  inches  with  a  uniform  taper  from  the  end 
of  the  pin  down  to  the  shoulder  and  with  the  thread  cut  down  the  stem 
for  three  or  four  inches.  Furthermore,  any  increase  in  the  cost  of  insu- 
lators for  these  larger  threaded  ends  of  pins  would  no  doubt  be  a  small 
matter.  Some  excess  of  strength  in  the  stem  of  a  pin  over  that  of  its 
shank  is  to  be  desired,  for  the  stem  is  more  exposed  to  the  weather  and 
to  charring  by  leakage  currents  over  the  surface  of  the  insulator.  On 
high- voltage  lines,  this  charring  is  usually  worse  at  that  part  of  each  pin 
just  below  its  thread,  and  the  commonest  breaks  of  pins  on  these  lines 
leave  the  insulators  with  the  threaded  portions  of  their  pins  hanging  on 
the  wire,  while  the  remainder  of  each  pin  remains  on  the  cross-arm. 
From  the  tests  just  noted  it  is  evidently  poor  design  to  give  the  threaded 
portion  of  a  pin  a  short  length  of  uniform  diameter,  and  then  to  increase 
the  diameter  at  once  by  a  shoulder,  as  was  done  with  the  pins  on 
the  Colgate  and  Oakland  line.  This  design  evidently  leads  to  failure 
of  pins  by  splitting  from  the  lower  end  of  the  threads.  The  better 
design  is  the  more  common  one  which  gives  the  stem  of  the  pin  a  uniform 
taper  from  the  shoulder  to  the  top.  Where  the  line  wire  is  secured  to 
the  top  of  its  insulator,  anywhere  from  one  to  three  inches  above  the  top 
of  the  pin,  there  is  a  strong  tendency  for  the  insulator  to  tip  on  its  pin, 
and  this  tendency  is  more  effectively  met  the  longer  the  joint  between 
the  pin  and  insulator. 


CHAPTER  XXIII. 

STEEL  TOWERS. 

STEEL  towers  are  rapidly  coming  into  use  for  the  support  of  electric 
transmission  lines  that  deliver  large  units  of  energy  at  high  voltages  to 
long  distances  from  water-powers. 

One  case  of  this  sort  is  the  seventy-five-mile  transmission  of  24,000 
horse-power  at  60,000  volts  from  Niagara  Falls  to  Toronto.  Another 
example  may  be  seen  in  the  seventy-five-mile  line  of  steel  towers  which 
carries  transmission  circuits  of  60,000  volts  to  Winnipeg.  Guanajuato, 
Mexico,  which  is  said  to  have  produced  more  silver  than  any  other  city 
in  the  world,  receives  some  3,300  electric  horse-power  over  a  60,000- 
volt  transmission  line  one  hundred  miles  long  on  steel  towers.  Between 
Niagara  Falls  and  Lockport  the  electric  circuits  now  being  erected  are 
supported  on  steel  towers.  On  a  transmission  line  eighty  miles  long 
in  northern  New  York,  for  which  plans  are  now  being  made,  steel 
towers  are  to  support  electric  conductors  that  carry  current  at  60,000 
volts. 

For  the  elevations  above  ground  at  which  it  is  common  to  support  the 
conductors  of  transmission  lines — that  is,  from  twenty-five  to  fifty  feet — 
a  steel  tower  will  cost  from  five  to  twenty  times  as  much  as  a  wooden  pole 
in  various  parts  of  the  United  States  and  Canada.  It  follows  at  once 
from  this  fact  that  there  must  be  cogent  reasons,  apart  from  the  matter 
of  first  cost,  if  the  general  substitution  of  steel  towers  for  wooden  poles 
on  transmission  lines  is  to  be  justified  on  economic  grounds.  During 
fifteen  years  the  electric  transmission  of  energy  from  distant  water- 
powers  to  important  centres  of  population  has  grown  from  the  most 
humble  beginnings  to  the  delivery  of  hundreds  of  thousands  of  horse- 
power in  the  service  of  millions  of  people,  and  the  lines  for  this  work  are 
supported,  with  very  few  exceptions,  on  wooden  poles.  Among  the 
transmissions  of  large  powers  over  long  distances  at  very  high  voltages 
that  have  been  in  successful  operation  during  at  least  several  years  with 
wooden  pole  lines  are  the  following:  the  60,000- volt  circuit  that  trans- 
mits some  13,000  horse-power  from  Electra  station  across  the  State  of 
California  to  San  Francisco,  a  distance  of  147  miles,  is  supported  by 

306 


STEEL  TOWERS.  307 

wooden  poles.  In  the  same  State,  the  transmission  line  142  miles  long 
between  Colgate  power-house  and  Oakland,  at  60,000  volts,  and  with  a 
capacity  of  about  15,000  horse-power,  hangs  on  wooden  poles,  save  at 
the  span  nearly  a  mile  long  over  the  Straits  of  Carquinez.  Wood  is  used 
to  carry  the  two  5 5,000- volt  circuits  that  run  sixty-five  miles  from  the 
io,ooo-horse-power  station  at  Canon  Ferry  on  the  Missouri  River  to 
Butte.  Between  Shawinigan  Falls  and  Montreal,  a  distance  of  eighty- 
three  miles,  the  conductors  that  operate  at  about  50,000  volts  are  car- 
ried on  wooden  poles.  Electrical  supply  in  Buffalo  to  the  amount  of 
30,000  horse-power  depends  entirely  on  circuits  from  Niagara  Falls  that 
operate  at  22,000  volts  and  are  supported  on  lines  of  wooden  poles. 

In  the  operation  of  these  and  many  other  high-voltage  transmissions 
during  various  parts  of  the  past  decade  some  difficulties  have  been  met 
with,  but  they  have  not  been  so  serious  as  to  prevent  satisfactory  service. 
Nevertheless,  it  is  now  being  urged  that  certain  impediments  that  are 
met  in  the  operation  of  transmission  systems  would  be  much  reduced 
by  the  substitution  of  steel  towers  for  wooden  poles,  and  it  is  even  sug- 
gested that  perhaps  the  first  cost,  and  probably  the  last  cost,  of  a  trans- 
mission line  would  be  less  with  steel  than  with  wood  for  supports.  The 
argument  for  steel  in  the  matter  of  costs  is  that  while  a  tower  requires  a 
larger  investment  than  a  pole,  yet  the  smaller  number  of  towers  as  com- 
pared with  that  of  poles  may  reduce  the  entire  outlay  for  the  former  to 
about  that  for  the  latter.  More  than  this,  it  is  said  that  the  lower  de- 
preciation and  maintenance  charges  on  steel  supports  will  make  their 
final  cost  no  greater  than  that  of  wooden  poles. 

In  the  present  state  of  the  market,  steel  towers  can  be  had  at  from 
three  to  three  and  one-half  cents  per  pound,  and  the  cost  of  a  steel  tower 
or  pole  will  vary  nearly  as  its  weight.  During  the  first  half  of  1904  the 
quotations  on  tubular  steel  poles  to  the  Southside  Suburban  Railway 
Company,  of  Chicago,  were  between  the  limits  just  stated.  That  com- 
pany ordered  some  poles  built  up  of  steel  sections  about  that  time  at  a 
trifle  less  than  three  cents  per  pound.  Each  of  these  poles  was  thirty 
feet  long  and  weighed  616  pounds,  so  that  its  cost  was  about  eighteen 
dollars  (xxi,  A.  I.  E.  E.,  754).  For  a  forty-five-foot  steel  pole  to  carry 
a  pair  of  n,ooo-volt,  three-phase  circuits  along  the  New  York  Central 
electric  road  the  estimated  cost  was  eighty  dollars  in  the  year  last  named 
(xxi,  A.  I.  E.  E.,  753).  On  the  loo-mile  line  to  Guanajuato,  Mexico, 
above  mentioned,  the  steel  towers  were  built  up  of  3"  x  3"  x  T3g-''  angles 
for  legs,  and  were  stayed  with  smaller  angle  sections  and  rods.  Each  of 
these  towers  has  four  legs  that  come  together  near  the  top,  is  forty  feet 


3o8     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

high,  weighs  about  1,500  pounds,  and  carries  a  single  circuit  composed 
of  three  No.  i  B.  &  S.  gauge  hard-drawn  copper  cables.  The  weight  of 
each  of  these  cables  is  1,340  pounds  per  mile,  and  the  forty-foot  towers  are 
spaced  440  feet  apart,  or  twelve  per  mile,  over  nearly  the  entire  length  of 
line.  At  three  cents  per  pound,  the  lowest  figure  at  which  these  towers 
could  probably  be  secured  for  use  in  the  United  States,  the  approximate 
cost  of  each  would  be  forty-five  dollars.  Between  Niagara  Falls  and 
Lockport  each  of  the  steel  towers  that  is  to  carry  a  single  three-phase 
transmission  circuit  has  three  legs  built  up  of  tubing  that  tapers  from  two 
and  one-half  inches  to  smaller  sizes  and  is  braced  at  frequent  intervals. 
The  height  of  these  towers  is  forty-nine  feet,  and  the  weight  of  each  is 
2,800  pounds.  At  three  cents  per  pound  the  cost  of  each  tower  amounts 
to  eighty-four  dollars.  For  a  long  transmission  line  in  northern  New 
York  bids  were  recently  had  on  towers  forty-five  feet  high  to  carry  six 
wires,  and  the  resulting  prices  were  #100  to  #125  each  for  a  tower  weigh- 
ing about  3,000  pounds.  On  the  line  between  Niagara  Falls  and  To- 
ronto the  standard  tower  holds  the  lowest  cables  40  feet  above  ground 
at  the  insulators,  has  a  weight  of  2,360  pounds,  and  would  cost  #70,80 
at  3  cents  per  pound. 

In  January,  1902,  four  steel  towers  were  purchased  to  support  trans- 
mission circuits  for  two  spans  of  132  feet  each  over  the  Chambly  Canal, 
near  Chambly  Canton,  Quebec.  Each  pair  of  these  towers  was  required 
to  support  eleven  No.  2-0  B.  &  S.  gauge  bare  copper  wires  with  the 
span  of  132  feet  between  them.  The  vertical  height  of  each  of  these  four 
towers  is  144  feet  above  the  foundation,  and  they  were  designed  for  a 
maximum  stress  in  any  member  of  not  more  than  one-fourth  of  its  ulti- 
mate strength,  with  wires  coated  to  a  diameter  of  one  inch  with  ice  and 
under  wind  pressure.  For  these  four  steel  towers  erected  on  foundations 
supplied  by  the  purchasers  the  price  was  #4,670,  and  the  contract  called 
for  a  weight  in  the  four  towers  of  not  less  than  121,000  pounds.  On  the 
basis  of  this  weight  the  cost  of  the  towers  erected  on  foundations  was 
3.86  cents  per  pound. 

With  these  examples  of  the  cost  of  steel  towers  a  fair  idea  may  be  gotten 
of  the  relative  cost  of  wooden  poles.  For  poles  of  cedar  or  other  desir- 
able wood  thirty-five  feet  long  and  with  eight-inch  tops  fitted  with  either 
one  or  two  cross-arms  an  estimated  cost  of  five  dollars  each  is  ample  to 
cover  delivery  at  railway  points  over  a  great  part  of  the  United  States 
and  Canada.  This  size  of  pole  has  been  much  used  on  the  long,  high- 
voltage  transmission  systems  that  involve  large  power  units  and  use 
heavy  conductors.  Examples  of  lines  where  such  poles  are  used  may 


STEEL  TOWERS.  309 

be  seen  between  Niagara  Falls  and  Buffalo,  between  Colgate  power- 
house and  Oakland,  and  between  Canon  Ferry  and  Butte.  Of  course 
some  longer  poles  were  used  in  special  locations,  like  the  crossing  of  steam 
railways,  but  it  is  also  true  that  on  the  lines  supported  by  steel  towers 
such  locations  make  exceptionally  high  towers  necessary.  The  thirty- 
five-foot  poles  will  hold  the  electric  lines  about  as  high  above  the  ground 
level  as  the  forty-nine-foot  towers  on  the  Niagara  Falls  and  Toronto 
transmission,  because  the  former  will  be  set  so  much  closer  together. 
On  the  line  just  named  the  regular  minimum  distance  of  the  electric 
cables  above  the  ground  level  at  the  centres  of  spans  is  twenty-five  feet. 
The  standard  towers  on  this  line  carry  the  lower  electric  cables  forty  feet 
above  the  ground  at  the  insulators,  and  it  was  thought  desirable  to  allow 
a  sag  of  fifteen  feet  at  the  centres  of  the  regular  spans  of  four  hundred 
feet  each.  On  these  towers  the  conductors  that  form  each  three-phase 
circuit  are  six  feet  apart,  and  lines  drawn  between  the  three  cables 
form  the  sides  of  an  equilateral  triangle.  With  a  pin  fourteen  and  three- 
fourths  inches  long  like  that  used  on  these  steel  towers,  and  one  con- 
ductor at  the  top  of  a  thirty-five-foot  pole,  where  the  other  two  are 
supported  by  a  cross-arm  five  feet  three  inches  below,  giving  six  feet 
between  cables,  the  lower  cables  are  held  by  their  insulators  twenty-six 
feet  above  the  ground,  when  the  poles  are  set  five  feet  deep.  Between 
thirty-five-foot  poles  one  hundred  feet  is  a  very  moderate  span,  and  one 
that  is  exceeded  in  a  number  of  instances.  Thus  on  the  142-mile  line 
from  Colgate  power-house  to  Oakland  the  thirty-five-foot  poles  are  132 
feet  apart,  and  one  line  of  these  poles  carries  three  conductors  of  133,- 
ooo-circular-mil  copper,  while  the  other  pole  line  has  three  aluminum 
cables  of  168,000  circular  mils.  On  the  later  transmission  line  from 
Niagara  Falls  to  Buffalo,  which  was  designed  for  three-phase  circuits 
of  5oo,ooo-circular-mil  cable,  the  regular  distance  between  the  thirty- 
five-foot  poles  is  140  feet. 

A  maximum  sag  of  twenty-four  inches  between  poles  100  feet  apart 
under  the  conditions  named  above  brings  the  lowest  points  of  the  wire 
twenty-four  feet  above  the  ground.  The  steel  towers  on  the  line  to 
Guanajuato  being  only  forty  feet  in  length,  and  spaced  440  feet  apart, 
it  seems  that  the  distance  of  conductors  from  the  ground  at  the  centres  of 
spans  is  probably  no  greater  than  that  just  named.  Particular  attention 
is  called  to  this  point  because  it  has  been  suggested  that  the  use  of  steel 
towers  would  carry  cables  so  high  that  wires  and  sticks  could  not  be 
thrown  onto  them.  It  thus  appears  that  thirty-five-foot  wooden  poles 
set  one  hundred  feet  apart  will  allow  as  much  distance  between  con- 


310    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

ductors,  and  still  keep  their  lowest  points  as  far  above  the  ground,  as 
will  forty-  to  forty-nine-foot  towers  placed  four  hundred  feet  or  more 
apart.  The  two  lines  that  have  their  conductors  further  apart  perhaps 
than  any  others  in  the  world  are  the  one  from  Canon  Ferry  to  Butte,  on 
thirty-five-foot  wooden  poles,  and  the  one  to  Guanajuato,  on  steel 
towers.  In  each  of  these  cases  the  cables  are  seventy-eight  inches  apart 
at  the  corners  of  an  equilateral  triangle.  With  steel  towers  four  hundred 
feet  or  wooden  poles  one  hundred  feet  apart,  four  of  the  latter  must 
be  used  to  one  of  the  former.  At  #5  per  pole  this  requires  an  invest- 
ment of  #20  in  poles  as  compared  with  at  least  #45  for  a  tower  like 
those  on  the  Guanajuato  line,  $84  for  a  tower  like  those  on  the  line  from 
Niagara  Falls  to  Lockport,  or  $70  for  one  of  the  towers  on  the  Niagara 
and  Toronto  line.  Each  of  the  towers  on  the  line  to  Toronto  carries  two 
three-phase  circuits,  and  the  least  distance  between  cables  is  six  feet. 
To  reach  the  same  result  as  to  the  distance  between  conductors  with  the 
two  circuits  on  poles,  it  would  be  desirable  to  have  two  pole  lines,  so 
that  $40  would  represent  the  investment  in  the  poles  to  displace  one 
tower  for  two  circuits^  The  older  pole  line  between  Niagara  Falls  and 
Buffalo  carries  two  three-phase  circuits  on  two  cross-arms,  and  the 
35o,ooo-circular-mil  copper  cables  of  each  circuit  are  at  the  angles  of 
an  equilateral  triangle  whose  sides  are  each  three  feet  long.  In  this 
case,  however,  the  electric  pressure  is  only  22,000  volts. 

The  costs  above  named  for  poles  and  towers  include  nothing  for 
erection.  Each  tower  has  at  least  three  legs  and  more  commonly  four, 
and  owing  to  the  heights  of  towers  and  to  the  long  spans  they  support 
it  is  the  usual  practice  to  give  each  leg  a  footing  of  cement  concrete.  It 
thus  seems  that  the  number  of  holes  to  be  dug  for  a  line  of  towers  is 
nearly  or  quite  as  great  as  that  for  a  line  of  poles,  and  considering  the 
concrete  footings  the  cost  of  erecting  the  towers  is  probably  greater  than 
that  for  the  poles.  With  wooden  poles  about  four  times  as  many  pins 
and  insulators  are  required  as  with  steel  towers,  or  say  twelve  pins  and 
insulators  on  poles  instead  of  three  on  a  tower.  For  circuits  of  50,000 
to  60,000  volts  the  approximate  cost  of  each  insulator  with  a  steel  pin 
may  be  taken  at  #1.50,  so  that  the  saving  per  tower  reaches  not  more 
than  #13.50  in  this  respect.  In  the  labor  of  erecting  circuits  there  may 
be  a  small  advantage  in  favor  of  the  towers,  but  the  weight  of  the  long 
spans  probably  offsets  to  a  large  extent  any  grain  of  time  due  to  fewer 
points  of  support. 

An  approximate  conclusion  from  the  above  facts  seems  to  be  that  a 
line  of  steel  towers  will  probably  cost  from  1.5  to  twice  as  much  as  a  line 


STEEL  TOWERS.  311 

or  lines  of  wooden  poles  to  support  the  same  number  of  conductors  the 
same  distance  apart,  even  when  the  saving  of  pins  and  insulators  is 
credited  to  the  towers.  This  conclusion  applies  to  construction  over  a 
large  part  of  the  United  States  and  Canada.  It  is  known  that  wooden 
poles  of  good  quality  retain  enough  strength  to  make  them  reliable  as 
supports  during  ten  or  fifteen  years,  and  it  is  doubtful  whether  steel 
towers  will  show  enough  longer  life  to  more  than  offset  their  greater  first 
cost.  It  may  be  noted  here  that  any  saving  in  the  cost  of  insulators  or 
other  advantage  that  there  may  be  in  spans  four  hundred  feet  or  more 
long  can  be  as  readily  secured  with  wooden  as  with  steel  supports. 
With  these  long  spans  the  requirements  are  greater  height  and  strength 
in  the  line  supports,  and  these  can  readily  be  obtained  in  structures 
each  of  which  is  formed  of  three  or  four  poles  with  cross-braces.  Such 
wooden  structures  have  long  been  in  use  at  certain  points  on  transmission 
lines  where  special  long  spans  were  necessary  or  where  there  were  large 
angular  changes  of  direction.  In  those  special  cases  where  structures  75 
to  1 50  or  more  feet  in  height  are  necessary  to  carry  a  span  across  a 
waterway,  as  at  the  Chambly  Canal  above  mentioned,  steel  is  generally 
more  desirable  than  wood  because  poles  of  such  lengths  are  not  readily 
obtainable.  Neither  present  proposals  nor  practice,  however,  con- 
templates the  use  of  steel  towers  having  a  length  of  more  than  forty  to 
fifty  feet  on  regular  spans. 

Much  the  strongest  argument  in  favor  of  steel  towers  for  transmis- 
sion lines  is  that  these  towers  give  a  greater  reliability  of  operation  than 
do  wooden  poles.  It  is  said  that  towers  will  act  as  lightning-rods  and 
thus  protect  line  conductors  and  station  apparatus.  As  to  static  and  in- 
ductive influences  from  lightning,  it  is  evident  that  steel  towers  can  give 
no  protection.  If  each  tower  has  an  especial  ground  connection  it  will 
probably  protect  the  line  to  some  extent  against  direct  lightning  strokes, 
but  there  is  no  reason  to  think  that  this  protection  will  be  any  greater 
than  that  given  by  well-grounded  guard  wires,  or  even  by  a  wire  run 
from  a  ground  plate  to  the  top  of  each  pole  or  wooden  tower.  If  a  direct 
lightning  stroke  passes  from  the  line  conductors  to  a  wooden  support  it 
frequently  breaks  the  insulator  on  that  support,  and  the  pole  is  often 
shattered  or  burned.  Such  a  result  does  not  necessarily  interrupt  the 
transmission  service,  however,  as  the  near-by  poles  can  usually  carry  the 
additional  strain  of  the  line  until  a  new  pole  can  be  set.  Quite  a  differ- 
ent result  might  be  reached  if  lightning  or  some  other  cause  broke  an 
insulator  on  a  steel  tower,  and  thus  allowed  one  of  the  electric  cables  to 
come  into  contact  with  the  metal  structure,  as  the  conductor  would  then 


3i2     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

probably  be  burned  in  two.  To  repair  a  heavy  cable  thus  severed  where 
the  spans  were  as  much  as  400  feet  long  would  certainly  require  some 
little  time.  Where  a  conductor  in  circuits  operating  at  20,000  to  35,000 
volts  has  in  many  cases  dropped  onto  a  wooden  cross-arm,  it  has  often 
remained  there  without  damage  until  discovered  by  the  line  inspector, 
but  no  such  result  could  be  expected  with  steel  towers  and  cross-arms 
(xxi,  A.  I.  E.  E.,  760).  Where  steel  towers  are  employed  it  would  seem 
to  be  safer  to  use  wooden  cross-arms,  for  the  reasons  just  stated.  This 
is,  in  fact,  the  practice  on  the  steel  towers  before  named  that  support 
25,ooo-volt  circuits  over  the  Chambly  Canal,  and  also  on  the  steel  towers 
that  carry  the  6o,ooo-volt  circuits  from  Colgate  power-house  over  the 
mile-wide  Straits  of  Carquinez. 

On  the  40, ooo- volt  transmission  line  between  Gromo  and  Nembro, 
Italy,  where  timber  is  scarce  and  steel  is  cheap,  both  the  poles  and  cross- 
arms  are  of  wood.  It  is  thought  that  the  comparatively  small  number 
of  insulators  used  where  a  line  is  supported  at  points  about  four  hundred 
feet  apart  should  contribute  to  reliability  in  operation,  but  insulators 
now  give  no  more  trouble  than  other  parts  of  the  line,  and  the  leakage 
of  energy  over  their  surfaces  is  very  small  in  amount,  as  was  shown  in 
the  Teluride  tests.  Whatever  benefits  are  to  be  had  from  long  spans 
are  as  available  with  wooden  as  with  steel  supports,  and  at  less  cost. 

One  advantage  of  steel  towers  over  wooden  poles  or  structures  is 
that  the  former  will  not  burn  and  are  probably  not  subject  to  destruc- 
tion by  lightning.  Where  a  long  line  passes  over  a  territory  where  there 
is  much  brush,  timber  or  long  grass,  the  fact  that  steel  towers  will  not 
burn  may  make  their  choice  desirable.  In  tropical  countries  where  in- 
sects rapidly  destroy  wooden  poles  the  use  of  steel  towers  may  be  highly 
desirable  even  at  much  greater  cost,  and  such  a  case  was  perhaps  pre- 
sented on  the  line  to  Guanajuato,  Mexico. 

Mechanical  failures  of  wooden  insulator  pins  have  been  far  more  com- 
mon than  those  of  poles,  both  as  a  direct  result  of  the  line  strains  and 
because  such  pins  are  often  charred  and  weakened  by  the  leakage  of 
energy  from  the  conductors.  For  these  reasons  the  general  use  of  iron 
or  steel  pins  for  the  insulators  of  long  lines  operating  at  high  voltages 
seems  desirable.  Such  pins  are  now  used  to  support  the  insulators  on 
a  number  of  lines  with  wooden  poles  and  cross-arms,  among  which  may 
be  mentioned  the  forty-mile,  3O,ooo-volt  transmission  between  Spier 
Falls  and  Albany  and  the  forty-five-mile  28,ooo-volt  line  from  Bear 
River  to  Ogden,  Utah.  Iron  or  steel  pins  add  very  little  to  the  cost  of  a 
line,  and  materially  increase  its  reliability.  One  of  the  cheapest  and 


STEEL  TOWERS.  313 

best  forms  of  steel  pins  is  that  swaged  from  a  steel  pipe  and  having  a 
straight  shank  and  tapering  stem  with  no  shoulder.  A  pin  of  this  sort 
for  the  4oo-foot  spans  of  i9O,ooo-circular-mil  copper  cable  on  the  line 
from  Niagara  Falls  to  Toronto  measures  three  and  one-quarter  inches 
long  in  the  shank,  eleven  and  one-half  inches  in  the  taper,  and  has  di- 
ameters of  two  and  three-eighths  inches  at  the  larger  and  one  and  one- 
eighth  inches  at  the  smaller  end.  On  spans  under  150  feet  between 
wooden  poles  pins  of  this  type  but  with  a  much  smaller  diameter 
could  be  used  to  advantage. 

On  long  transmission  lines  where  the  amount  of  power  involved  is 
very  large  the  additional  reliability  to  be  had  with  steel  towers  is  prob- 
ably great  enough  to  justify  their  use.  For  the  great  majority  of  powrer 
transmissions,  however,  it  seems  probable  that  wooden  poles  or  struc- 
tures will  long  continue  to  be  much  the  cheaper  and  more  practicable 
form  of  support. 

The  line  of  steel  towers  on  a  private  right  of  way  seventy-five  miles 
long,  carrying  two  circuits  for  the  transmission  of  24,000  horse-power  at 
60,000  volts  from  Niagara  Falls  to  Toronto,  is  one  of  the  most  prom- 
inent examples  of  this  type  of  construction. 

Eventually  there  will  be  two  rows  of  steel  towers  along  the  entire 
length  of  the  line. 

On  the  straight  portions  of  the  line  the  steel  towers  are  regularly 
erected  400  feet  apart,  but  on  curves  the  distances  are  less  between  towers, 
so  that  their  total  number  is  about  1,400  for  each  line.  Standard  curving 
along  the  line  requires  towers  placed  50  feet  apart,  and  a  change  in  the 
direction  of  not  more  than  ten  degrees  at  each  tower,  except  at  the  be- 
ginning and  end  of  the  curve,  where  the  change  in  direction  is  three 
degrees.  When  the  change  in  the  direction  of  the  line  is  not  more  than 
six  degrees,  the  corresponding  spans  allowed  with  each  change  are  as 
follows: 

Degrees  change.  Feet  of  span.  Degrees  change.  Feet  of  span. 

%  300  3%  219 

i  286  4  205 

1%  273  4%  192 

*  259  5  178 

2%  246  s«  165 

3  232  6  151 

At  some  points  along  the  line  conditions  require  a  span  between 
towers  of  more  than  400  feet,  the  regular  distance  for  straight  work. 
One  example  of  this  sort  occurs  at  Twelve -Mile  Creek,  where  the  stream 


314    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

has  cut  a  wide,  deep  gorge  in  the  Erie  plateau.     At  this  point  the  lines 
make  a  span  of  625  feet  between  towers. 

The  regular  steel  tower  used  in  this  transmission  measures  46  feet 
in  vertical  height  from  its  foot  to  the  tops  of  the  lower  insulators,  and  51 
feet  3  inches  to  the  tops  of  the  higher  insulators.  The  lower  six  feet  of 
this  tower  are  embedded  in  the  ground,  so  that  the  tops  of  the  insulators 
measure  about  40  feet  and  45  feet  3  inches  respectively  above  the  earth. 


FIG.  94.— Transposition  Tower  (Second  Tower). 

At  the  ground  the  tower  measures  14  feet  at  right  angles  to  the  trans- 
mission line  and  12  feet  parallel  with  it.  The  width  of  each  tower  at 
the  top  is  12  feet  at  right  angles  to  the  line,  and  the  two  sides  having 
this  width  come  together  at  points  about  40  feet  above  the  ground. 
Between  the  two  L  bars  thus  brought  nearly  together,  at  each  side  of  a 
tower  a  piece  of  extra  heavy  3 -inch  steel  pipe  is  bolted  so  as  to  stand  in 
a  vertical  position.  Each  piece  of  this  pipe  is  about  3^  feet  long  and 
carries  a  steel  insulator  pin  at  its  upper  end.  The  two  pieces  of  pipe 
thus  fixed  on  opposite  sides  of  the  top  of  a  tower  carry  the  two  highest 
insulators.  For  the  other  four  insulators  of  each  tower,  pins  are  fixed 
on  a  piece  of  standard  4-inch  pipe  that  serves  as  a  cross-arm,  and  is 


STEEL  TOWERS. 


bolted  in  a  horizontal  position  between  the  two  nearly  rectangular 
sides  of  each  tower,  at  a  point  two  feet  below  the  bolts  that  hold  the 
vertical  3-inch  pipes,  already  named,  in  position.  Save  for  the  two  short 
vertical  and  one  horizontal  pipe,  and  the  pins  they  support,  each  tower 
is  made  up  of  L-shaped  angle-bars  bolted  together.  Each  of  the  two 


3  Bztra 
*e»v,  pipe 


ussct  pi 


1 


FIG.  95.— Elevations  and  Plan  of  Tower. 

nearly  rectangular  sides  of  a  tower  consists  of  two  L  bars  at  its  two 
edges,  three  L  bars  for  cross-braces  at  right  angles  to  the  edges,  and 
four  diagonal  braces  also  formed  of  L  bars.  The  lower  halves  of  the  L 
bars  at  the  edges  of  each  side  of  a  tower  have  sections  of  3"  x  3"  x  J",  and 
the  upper  halves  have  sections  of  3"  x  3"  x  3-1 6".  This  last-named  cross- 
brace  and  the  other  two  cross-braces  have  a  common  section  of  2"  x  i  J" 
x  y.  For  the  lower  set  of  diagonal  braces  the  common  section  is  2  J"  x 
2"  x  £",  and  the  upper  set  has  a  section  of  2"  x  ij"  x  \"  in  each  member. 


3i6    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


r 


FIGS.  96,  97,  98.— Raising  Towers  on  Niagara  Transmis- 
sion Line. 


At  the  level  of  the  lowest 
cross-braces  the  two  rec- 
tangular sides  of  a  tower 
are  tied  together  by  one 
member  of  2"  x  ij*  x  J" 
of  L  section  and  at  right 
angles  to  the  sides,  and  by 
two  diagonal  braces  of  f " 
round  rod  between  the 
corners  of  the  tower.  On 
each  of  its  two  triangular 
sides  a  tower  has  four 
horizontal  braces  and 
three  sets  of  diagonal 
braces.  The  two  upper 
horizontal  braces  are  of 
2"  x  i£"  x  y  L  section, 
and  the  lowest  is  the 
same,  but  the  remaining 
horizontal  brace  has  a 
section  of  2^"  x  2"  x  J". 
Bars  of  2"  x  ij"  x  J"  L 
section  are  used  for  the 
two  upper  sets  of  diag- 
onal braces,  and  bars  of 
2  J"  x  2"  x  \"  for  the  lower 
set.  In  addition  to  the 
cross-braces  named,  each 
triangular  side  of  a  tower 
near  the  top  of  the  corner 
bars  has  two  short  cross- 
pieces  with  the  common 
L  section  of  3!"  X3^x 
f ",  one  just  above  and  the 
other  just  below  the  cross- 
arm  of  4-inch  pipe  to 
hold  it  in  place.  At  the 
bottom  of  each  of  the 
four  corner  bars  of  a 
tower  a  foot  is  formed 


STEEL  TOWERS.  317 

by  riveting  a  piece  of  3"  x  Y  L  section  and  1 5  inches  long  at  right 
angles  to  the  corner  bar.  On  one  corner  bar  of  each  tower  there  are 
two  rows  of  steel  studs  for  steps,  one  row  being  located  in  each  flange 
of  the  L  section.  On  the  same  flange  these  steps  are  two  feet  apart, 


FIG.  99.— One  of  the  Towers  in  Position. 


but  taking  both  flanges  they  are  only  one  foot  apart.     Every  part  of 
each  steel  tower  is  heavily  galvanized. 

The  labor  of  erecting  these  steel  towers  was  reduced  to  a  low  figure 
by  the  method  employed,  as  shown  in  the  accompanying  illustration. 
Each  tower  was  brought  to  the  place  where  it  was  to  stand  with  its 


3i8    ELECTRIC  TRANSMISSION  OF  WATER-POWER. 


parts  unassembled.  For  erecting  the  towers  a  four-wheel  wagon  with 
a  timber  body  about  thirty  feet  long  was  used.  When  it  was  desired 
to  raise  a  tower,  two  of  the  wheels,  with  their  axle,  were  detached  from 
the  timber  body  of  the  wagon,  and  this  body  was  then  stood  on  end  to 
serve  as  a  sort  of  derrick.  This  derrick  was  guyed  at  its  top  on  the  side 


Bight  of  Way 
FIG.  ioo. — Steel  Tower  for  Transmission  Line. 


!     \ 


away  from  the  tower,  and  a  set  of  blocks  and  tackle  was  then  connected 
to  the  top  of  the  derrick  and  to  the  tower  at  a  point  about  one-fourth 
of  the  distance  from  its  top.  A  rope  from  this  set  of  blocks  ran  through 
a  single  block  fixed  to  the  base  of  the  derrick  and  then  to  a  team  of 
horses.  On  driving  these  horses  away  from  the  derrick  the  steel  tower 
was  gradually  raised  on  the  two  legs  of  one  of  its  rectangular  sides 
until  it  came  to  a  vertical  position.  The  next  operation  was  to  bring 
the  legs  of  the  tower  into  contact  with  the  extension  pieces  that  were 
fixed  in  the  earth  and  then  bolt  them  together. 

The  tops  of  the  three  pins  that  carry  the  insulators  for  each  three- 
phase  circuit  are  at  the  corners  of  an  equilateral  triangle  (Fig.  ioo),  each 
of  whose  sides  measures  six  feet.  The  six  steel  insulator  pins  used  on 
each  tower  are  exactly  alike,  and  each  is  swaged  from  extra  heavy  pipe. 
Each  finished  pin  is  2$  inches  in  diameter  for  a  length  of  3  J  inches,  and 
then  tapers  uniformly  to  a  diameter  of  ij  inch  at  the  top  through  a 
length  of  ni  inches.  This  gives  the  pin  a  total  length  of  14!  inches. 
In  the  larger  part  there  are  two  9-1 6-inch  holes  from  side  to  side,  and 
within  two  inches  of  the  top  there  are  three  circular  grooves  each  3-16 
inch  wide  and  1-16  inch  deep.  Forged  steel  sockets  of  two  types  are 
employed  to  attach  the  steel  pins  with  the  pipes.  Each  socket  is  made 
in  halves,  and  these  halves  are  secured  to  both  the  pipe  and  the  pin 
by  through  bolts.  Like  all  other  parts  of  the  towers,  these  steel  pins  and 


STEEL  TOWERS.  319 

sockets  are  heavily  galvanized.  On  each  of  the  four  corner  bars  of  a 
tower  the  lower  six  feet  of  its  length  is  secured  to  the  upper  part  by 
bolts  or  rivets.  This  lower  six  feet  of  each  corner  bar  is  embedded  in 
the  earth,  and  the  construction  just  named  makes  it  easy  to  replace  the 
bars  in  the  earth  when  corrosion  makes  it  necessary. 

Footings  for  each  tower  are  provided  by  digging  four  nearly  square 
holes  with  their  sides  at  approximately  45  degrees  with  the  direction  of 
the  transmission  line,  and  the  shortest  side  of  each  hole  at  least  two  feet 
long.  Centres  of  these  holes  are  14  feet  3  inches  apart  in  a  direction 
at  right  angles  to  the  line,  and  13  feet  9  inches  apart  parallel  with  the 
line.  In  hard-pan  each  one  of  the  holes  was  filled  to  within  2  feet  6 
inches  of  the  top  with  stones,  after  the  leg  of  the  tower  was  in  position, 
and  then  the  remainder  of  the  hole  was  filled  with  cement  grouting 
mixed  four  to  one. 

At  the  bottom  of  each  hole  in  marsh  land  a  wooden  footing  3  feet  x 
6  inches  x  24  inches  was  laid  flat  beneath  the  leg  of  the  tower,  and  then 
the  hole  was  filled  to  within  2\  feet  of  the  surface  with 'the  excavated 
material.  Next  above  this  filling  comes  a  galvanized  iron  gutter-pipe, 
four  inches  in  diameter,  and  filled  with  cement  about  the  leg  of  the 


Welland  Canal. 


FIG.  101. — Transmission  Line  at  Welland  Canal. 

tower  for  a  length  of  two  feet.     Outside  of  this  pipe  the  hole  is  made 
rounding  full  of  cement  grouting. 

At  some  points  along  the  transmission  line  exceptionally  high  towers 
are  necessary,  a  notable  instance  being  found  at  the  crossing  over  the 
Welland  Canal,  where  the  lowest  part  of  each  span  must  not  be  less  than 
150  feet  above  the  water.  For  this  crossing  two  towers  135  feet  high 
above  ground  are  used,  as  seen  in  Fig.  101.  Each  of  these  towers  is  de- 
signed to  carry  all  four  of  the  three-phase  power  circuits  that  are  eventu- 
ally to  be  erected  between  Niagara  Falls  and  Toronto.  For  this  purpose 
there  was  used  a  special  design  of  tower  with  a  width  of  about  48  feet 
at  right  angles  to  the  direction  of  the  line  below  the  top  truss,  and  a 
width  of  about  68.5  feet  at  that  truss  where  the  two  lower  conductors 
of  each  circuit  are  attached. 


320     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

With  all  spans  longer  than  400  feet,  a  tower  of  heavier  construction 
than  the  standard  type  is  used,  and  this  tower  provides  three  insulators 
for  the  support  of  each  conductor.  A  tower  of  this  type  that  supports 
the  lowest  conductors  about  40  feet  above  the  ground  level  has  its  corner 
bars  made  up  of  4"  x  4°  x  f"  and  4"  x  4"  x  5-16"  L  sections,  has  three 
cross-arms  of  extra  heavy  4-inch  pipe,  and  a  6-inch  vertical  standard  pipe 


FIG.  102.  -  Heavy  Tower  at  Credit  River. 

to  support  each  group  of  three  insulators  for  the  highest  conductor  of 
each  circuit.  Each  of  the  lower  conductors  of  a  circuit  on  this  tower 
is  supported  by  an  insulator  on  each  of  the  three  parallel  cross-arms. 
On  some  of  these  towers,  for  long  spans,  the  two  outside  insulators  for 
the  support  of  each  conductor  are  set  a  little  lower  than  the  insulator 
between  them. 

Angle  towers,  used  where  the  line  makes  a  large  change  in  direction 
at  a  single  point,  have  three  legs  on  each  rectangular  side,  a  width  of 
20  feet  on  each  of  these  sides  for  some  distance  above  the  ground,  and  a 
width  of  27  feet  2  inches  at  the  top.  In  these  towers  the  two  legs  on 


STEEL  TOWERS. 


321 


322     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

the  triangular  side  that  is  in  compression  are  each  made  up  of  four 
3"x3"x£"  L  sections  joined  by  i£"xj"  lattices  and  rivets.  Towers 
of  this  sort  are  used  near  the  Toronto  terminal-station,  where  the  line 
changes  35  degrees  at  a  single  point,  and  near  the  crossing  of  Twelve-' 
Mile  Creek,  where  the  angular  change  of  the  line  on  a  tower  is  45  de- 
grees. Close  to  each  terminal-station  and  division-house  the  trans- 
mission line  is  supported  by  terminal  towers.  These  towers  differ 
from  the  others  in  that  each  carries  insulators  for  only  three  conductors, 
and  these  insulators  are  all  at  the  same  level.  Each  terminal  tower  has 
nine  insulators,  arranged  in  three  parallel  rows  of  three  each  for  the  con- 
ductors of  a  single  circuit,  and  each  conductor  thus  has  its  strain  dis- 
tributed between  three  pins.  All  three  wires  of  a  circuit  are  held  40  feet 
above  the  ground  by  a  terminal  tower,  and  pass  to  their  entries  in  the 
wall  of  a  station  at  the  same  level.  As  these  terminal  towers  must  resist 
the  end  strain  of  the  line,  they  are  made  extra  heavy,  the  four  legs  each 
being  made  up  of  4"  x  4"  x  5-16"  and  4"  x  4"  x  I"  L  sections.  For  the 
three  cross-arms  on  one  of  these  towers  three  pieces  of  4-inch  pipe,  each 
15  feet  9  inches  long,  are  secured  at  its  top  with  their  parallel  centre 
lines  30  inches  apart  in  the  same  plane.  Each  of  these  pipes  carries 
three  insulator  pins  with  their  centres  7  feet  4^  inches  apart.  On  the 
bottom  of  each  leg  of  a  terminal  tower  there  is  a  foot,  formed  by  riveting 
on  bent  plates,  that  measure  15  and  18  inches,  respectively,  on  the  two 
longer  sides.  Each  foot  of  this  tower  is  set  in  a  block  of  concrete  5  feet 
square  that  extends  from  3.5  feet  to  7.5  feet  below  the  ground  level. 

Insulators  for  the  transmission  line,  which  are  illustrated  in  Fig.  104, 
are  of  brown,  glazed  porcelain,  made  in  three  parts,  and  cemented  to- 
gether. The  three  parts  consist  of  three  petticoats  or  thimbles,  each  of 
which  slips  over  or  into  one  of  the  others,  so  that  there  are  three  outside 
surfaces  and  three  interior  or  protected  surfaces  between  the  top  of  an 
insulator  and  its  pin. 

From  top  to  bottom  the  height  of  each  insulator  is  14  inches,  and 
this  is  also  the  diameter  of  the  highest  and  largest  petticoat.  The  next 
or  middle  petticoat  has  a  maximum  diameter  of  10  inches  a*nd  the 
lowest  petticoat  one  of  8  inches.  Cement  holds  the  lowest  petticoat  of 
the  insulator  on  one  of  the  steel  pins  previously  described,  and  in  this 
position  the  edge  of  the  lowest  petticoat  is  about  2  J  inches  from  the 
steel  support.  At  the  top  of  each  insulator  the  transmission  conductor 
is  secured,  and  the  shortest  distance  from  this  conductor  to  any  of  the 
steel  parts  through  the  air  is  about  17  inches. 

From  the  step-up  transformer  house  at  Niagara  Falls  to  the  terminal- 


STEEL  TOWERS. 


323 


station  at  Toronto,  a  distance  of  seventy-five  miles,  each  three-phase, 
60,000- volt,  25-cycle  circuit  on  the  steel  towers  is  made  up  of  three  hard- 
drawn  copper  cables  with  a  cross  section  of  190,000  circular  mils  each, 
and  is  designed  to  deliver  1 2,000  electric  horse-power  with  a  loss  of  ten 


FIG.  104.— Insulators. 

per  cent,  on  a  basis  of  100  per  cent  power  factor.  Six  equal  strands 
of  copper  make  up  each  cable,  and  this  wire  has  been  specially  drawn 
with  an  elastic  limit  of  more  than  35,000  pounds  and  a  tensile  strength 
of  over  55,000  pounds  per  square  inch.  This  cable  is  made  in  uniform 
lengths  of  3,000  feet,  and  these  lengths  are  joined  by  twisting  their  ends 
together  in  copper  sleeves,  and  no  solder  is  used.  No  insulation  is  used 
on  these  cables. 

Instead  of  a  tie-wire,  a   novel  clamp  is  employed   to   secure   the 


324     ELECTRIC  TRANSMISSION  OF  WATER-POWER. 

copper  cable  on  each  insulator.  This  complete  clamp  is  made  up  of 
two  separate  clamps  that  grasp  the  cable  at  opposite  sides  of  each  in- 
sulator and  of  two  half -circles  of  hard-drawn  copper  wire  of  0.187  inch 
diameter.  Each  half-circle  of  this  wire  joins  one-half  of  each  of  the 
opposite  clamps,  and  fits  about  the  neck  of  the  insulator  just  below  its 
head.  Two  bronze  castings,  one  of  which  has  a  bolt  extension  that 
passes  through  the  other,  and  a  nut,  make  up  each  separate  clamp. 
When  the  combined  clamp  is  to  be  applied,  the  sides  are  separated  by 
removing  the  nut  that  holds  them  together,  the  half-circles  are  brought 
around  the  neck  of  the  insulator,  and  each  of  the  side  clamps  is  then 
tightened  on  to  the  cable  by  turning  the  nut  that  draws  its  halves  to- 
gether. This  complete  clamp  can  be  applied  as  quickly  as  a  tie-wire, 
is  very  strong,  and  does  not  cut  into  the  cable. 

Each  of  the  regular  steel  towers  is  designed  to  withstand  safely  a 
side  strain  of  10,000  pounds  at  the  insulators,  or  an  average  of  1,666 
pounds  per  cable.  With  the  i9o,ooo-mil  cable  coated  to  a  depth  of 
J  inch  with  ice  and  exposed  to  a  wind  blowing  100  miles  per  hour,  the 
estimated  strains  on  each  steel  pin  for  different  spans  and  angular 
changes  in  the  direction  of  the  line  are  given  in  the  accompanying  table : 

POUNDS  STRAIN  ON  PINS,  >£-INCH  SLEET,  100  MILES  WIND. 


Span, 
feet. 


Degrees  and  Minutes. 


0.30 


1.30 


2.30 


3-30 


4-30 


5.30 


o.. 

100.. 
200.. 


700.. 

800.. 
900.. 

1,000.. 


o 

256 

512 

768 
1,024 

1,280 

1,536 

1,792 
2,048 


35 
291 


i,o59 


69 

1,093 

1,349 


2,117 

2.373 
2,629 


104 
360 
616 
872 
1,128 

1,640 
1,896 
2,152 
2,408 
2,664 


050 

906 

1,162 

1,418 

1,674 


173 

$ 

94i 
i,i97 
i,453 
1,709 
1,965 

2,221 

2,477 
2,733 


207 
463 
719 

975 


i,743 
i,999 
2,255 
2,511 
2,767 


242 

498 

754 

1,010 

1,266 

1,522 

2^034 
2.290 
2,546 
2,802 


$ 

1,044 
1,812 

2,068 
2,324 
2,580 

2,836 


311 

823 

1,079 

A-7 
2,103 

2-359 
2.615 
2,871 


345 
601 
857 
1,113 
i,369 
1,625 
i|88i 
2,137 
2,393 
2,649 
2,905 


1,916 
2,172 
2,428 

2;684 

2,940 


926 
1,182 

1,438 
1,694 
i,95o 
2,206 
2,462 
2,718 
2,974 


The  copper  cables  were  so  strung  as  to  have  a  minimum  distance 
from  the  ground  of  25  feet  at  the  lowest  points  of  the  spans.  In 
order  to  do  this  the  standard  steel  towers  that  hold  the  lower  cables 
40  feet  above  the  ground  level  at  the  insulators  are  spaced  at  varying 
distances  apart,  according  to  the  nature  of  the  ground  between  them. 
At  each  tower  the  upper  cable  of  each  circuit  is  5  feet  3  inches 
higher  than  the  two  lower  cables,  and  this  distance  between  the  eleva- 
tions of  the  upper  and  the  lower  cables  is  maintained  whatever  the 


STEEL  TOWERS. 


325 


amount  of  sag  at  the  centre  of  each  span.  If  there  is  a  depression  be- 
tween two  standard  towers  on  a  straight  portion  of  the  line,  the  sag  in 
the  centre  of  a  span  400  feet  long  may  be  as  much  as  18  feet.  Where 
a  rise  and  fall  in  the  ground  between  towers  make  it  necessary  to 
limit  the  sag  to  14  feet  in  order  to  keep  the  lowest  cables  25  feet  above 
the  highest  point  of  earth,  the  length  of  span  is  limited  to  350  feet. 
If  the  rise  and  fall  of  ground  level  between  towers  allow  a  sag  of  only 
ii  feet  with  the  lowest  cable  25  feet  above  the  earth,  the  length  of  span 
with  40-foot  towers  is  reduced  to  300  feet ;  and  if  for  a  like  reason  the 
sag  is  limited  to  8  feet,  the  span  may  only  be  250  feet. 

At  each  terminal  tower,  where  the  cables  are  secured  before  they 
pass  into  a  terminal-station,  the  three  insulators  for  each  cable  are  in  a 


FIG.  105.— Take-up  Arrangement  on  Terminal  Tower. 

straight  line  with  their  centres,  30  inches  apart.  When  a  line  cable 
reaches  the  first  insulator  of  the  three  to  which  it  is  to  be  attached  on 
one  of  ';hese  towers,  it  is  passed  around  the  neck  of  this  insulator  and 
then  secured  on  itself  by  means  of  two  clamps  that  are  tightened  with 
bolts  and  nuts.  See  Fig.  105.  The  cable  thus  secured  turns  up  and 
back  over  the  tops  of  the  three  insulators  and  goes  to  the  terminal-sta- 
tion. Around  the  neck  of  the  insulator  to  which  the  line  cable  has  been 
secured  in  the  way  just  outlined  a  short  detached  length  of  the  regular 
copper  cable  with  the  parts  of  a  turnbuckle  at  each  end  is  passed,  and 
this  same  piece  of  cable  also  passes  around  the  neck  of  the  next  insulator 
in  the  series  of  three.  By  joining  the  ends  of  the  turnbuckle  and  tight- 
ening it,  a  part  of  the  strain  of  the  line  cable  in  question  is  transferred 
from  the  first  to  the  second  insulator  of  the  series.  In  the  same  way  a 
part  of  the  strain  of  this  same  line  cable  is  transferred  from  the  second 
insulator  of  the  series  to  the  third,  or  one  nearest  to  the  terminal-station. 


INDEX. 


AIR-BLAST  cooled  transformers,  129 

Air-gap  data,  183 

Air  gaps,  number  in  series    to  stand 

given  voltage,  183 
Albany-Hudson  Ry.  Plant,  121 
Alternating  currents,  227 
Alternator  voltage,  118 
Alternators,  103 

data,  118 

for  high  voltage,  120 

inductor,  112 

types  of,  in 
Aluminum  as  a  conductor,  200,  209 

cables  in  use,  213 

conductor  joints,  206 

conductors,  27,  28 

corrosion  of,  211 

properties  of,  212 

soldered  joints,  206 

vs.  copper,  209 

wire,  cost  of,  29 

Amoskeag  Mfg.  Co.  plant,  51,  52 
Amsterdam  (N.  Y.)  plant,  121 
Anchor  ice,  59 
Anderson  (S.  C.)  plant,  121 
Apple  River  (Minn.)  plant,  i,  26,  27,  28, 
71,  97,  98,  99,  102,  118,  119,  124,  126, 
127,  134,  174,  187,  190,  192,  208,  245, 
264,  294 

Arc  lighting,  167 
Arcing,  46 
Automatic  regulators,  162 

BARBED  wire,  169,  175 
Belt  drive,  83,  107 
Bienne  plant  (Switzerland),  42 
Birchem  Bend,  57,  67,  79,  95,  97,  98,  102 
Blower  capacity  necessary  to  cool  trans- 
formers, 130 
Boosters,  133 
Boston-Worcester  Ry.  plants,  121 


Braces  for  cross-arms,  259 
Bronze  conductors,  200 
Brush  discharge,  281 
Buchanan  (Mich.)  plant,  88 
Building  materials,  95 
Bulls  Bridge  plant,  63 
Burrard  Inlet  (B.  C.)  plant,  in,  112 
Bus-bars,  142,  147 
dummy,  145 

CABLE  insulation,  195 

sheaths,  194 

ways,  140 
Cables,  aluminum,  212 

aluminum,  in  use,  213 

charging  current,  197 

cost  of,  188,  196 

for  alternating  current,  194 

high-voltage,  191 

paper  insulated,  196 

protection  against  electrolysis,  195 

rubber-covered,  195 

submarine,  192 

temperature  of,  198 

voltage  in,  190,  196 

Canadian-Niagara  Falls  Power  Co.,  121 
Canals,  51,  53 

long,  68 
Canon  City  plant,  26,  27,  28,  117,  118, 

127,  208 

Canon  Ferry  plant,  i,  3,  26,  27,  28,  46, 
49,  53,  62,  68,  69,  83,  89,  94,  95,  97, 

IO2,  IO5,  112,  113,  Il8,  119,  124,  125, 
126,  127,  130,  132,  134,  174,  208,  233, 
234,  245,  246,  249,  254,  257,  259,  268, 
272,  280,  282,  294,  295,  302 

Cedar  Lake  plant,  90 

Chambly  plant,  96,  no,  149,  156,  172, 

189,  249,  255,  256,  257,  267,  272,  287, 

294,  295,  311,  312 
Charging  current  for  cable,  197 


327 


328 


INDEX. 


Charring  of  pins,  276,  278 

Chaudiere  Falls  plant,  118 

Choke-coil  used  with  lightning  arresters, 
180 

Circuit  breakers,  135,  150 
breakers,  time  limit,  152 

Circuits,  selection  of,  233 

Coal,  price  of,  in  Salt  Lake  City,  8 

Colgate  plant,  i,  3,  26,  27,  28,  74,  82,  83, 
9°>  94,  97,  98>  99,  IQi>  102,  108,  112, 
113,  118,  127,  130,  132,  134,  187,  190, 
201,  206,  208,  213,  245,  246,  250,  254, 
257,  272,  277,  280,  282,  294,  295,  304, 

309 

Columbus  (Ga.)  plant,  83,  115 
Compounding,  160 
Compressive  strength  of  woods,  302 
Conductivity  of  the  conductor  metals, 

201 
Conductors,  200 

aluminum,  27,  28,  206 
aluminum,  properties  of,  212 
coefficients  of  expansion,  200 
corrosion  of,  211 
cost  of,  22,  29,  203,  204,  205 
cost  of  aluminum,  29 
cost  of  per  k.  w.,  28 
cost  of  copper,  29 
data,  204 

data  from  representative  transmis- 
sion plants,  208 
expansion  of  aluminum  and  copper, 

211 

melting  points,  200 
minimum  size  for  transmission  line, 

202 

properties  of  ideal,  200 
relative  conductivity,  201 
relative  cost  of,  20 
relative  properties  for  equal  lengths 

and  resistances,  204 
relative  strengths  for   given   area, 

203 

relative  weight  for  given  conductiv- 
ity, 202 

relative  weight  of,  202 
relative  weights  of  three-phase,  two- 
phase,  and  single-phase  lines,  220 


Conductors,  resistance  of,  225 

skin  effect,  206,  233 

weight  per  k.  w.,  27 
Conduits,  195 

radiation  loss  in,  198 

temperature  rise  in,  198 
Constant  current  regulator,  167 

transformer,  167 
Control  equipment  for  d.  c.  and  a.  c. 

plants,  35 
Copper  conductors,  200 

cost  of,  22 

vs.  aluminum,  209 

wire,  cost  of,  29 
Corrosion  of  conductors,  211 
Cross-arm  braces,  258 

iron,  284 

location  of,  257 

material,  258 
Cross-arms,  49,  256 
Crossings,  187 

DALES  plant  (White  River),  26,  27,  28, 

71,  134,  208 
Dams,  62 

Delta  connection,  131 
Depreciation,  u 
Design  of  power-plant,  83 
Dike,  60 

Direct  connection,  84 
Discharge,  static,  170 
Distribution  system,  158 
Draught  tubes,  79 
Dummy  bus-bars,  145 

EASTON  (Pa.)  plant,  121 
Edison  Co.  (Los  Angeles)  plant,  118 
Efficiency    constant-current    transmis- 
sion, 216 

curves,  motor-generator  set,  117 
of    constant-voltage    transmission, 

217 

of  transformers,  133 
relative,  of  a.  c.  and  d.  c.  transmis- 
sion, 35 

Electra  plant,  i,  3,  74,  82,  83,  92,  94,  97, 
98,  101,  102,  108,  112,  113,  118,  127, 

174,  206,  208,  212,  213,  233,  235,  236, 


INDEX. 


329 


245, 248,  253,  254,  256,  259, 272,  275, 
277, 280,  281, 282, 294,  295 

Electric  power,  market  for,  7 
Electrical   Development    Co.,   Niagara 

plant,  120 

Electricity  vs.  gas,  6 
Electrolysis,  195 
Energy  curves  of  hydro-electric  stations, 

!3 

electrical,  cost  of  at  switchboard, 

23 

Entrance  end  strain,  261,  325 
insulating  discs,  262 
into  buildings,  179 
of  lines,  179,  261,  265 
through  roof,  269 
wall  openings,  262 
Entries  for  transmission  lines,  261 
Expansion,  coefficient  of,  for  copper  and 

aluminum,  211 

coefficients  of,  for  various  conduc- 
tor metals,  200 

FARMINGTON  RIVER  (Conn.)  plant,  26, 
27,  28,  58,  118,  125,  134,  208,  212, 

213,  245 
Feeders,  143 
Ferranti  cables,  192 
Fire-proofing,  95 
Floor,  distance  from  roof  to,  95 

location  of,  79 

space,  12,  101,  102 

space  per  k.  w.  of  generators,  12 
Floors,  95 
Fog,  46,  277 
Fore-bay,  59,  60 
Foundations,  95 
Frequency,  113,  127 

effect  on  transformer  cost,  116 
Fuel,  price  of,  in  Salt  Lake  City,  8 
Fuses,  135,  150 

GARVINS  FALLS  plant,  56,  60,  79, 80, 94, 

96,  97,  102,  113,  145,  240,  294 
Gas  vs.  electricity,  6 
Gears,  84,  108 
Generators  (a.  c.),  103 
d.  c.  vs.  a.  c.,  31 


Generators,  belt-driven,  107 

capacity  of,  32 

compounding  of,  160 

cost  of,  40 

(a.  c.)  cost,  32 

(a.  c.)  data,  118 

direct-connnected  to  horizontal  tur- 
bines, 89 

to  impulse  wheels,  90 
connection  to  vertical  shafts, 
84 

(d.  c.)  field  excitation  of,  41 

floor  space,  101   • 
per  k.  w.,  12 

gear-driven,  108 

(a.  c.)  high -voltage,  120 

(d.  c.)  in  series,  31 

(d.  c.)  installation  of,  41 

insulation  of,  39,  45 

lightning  protection,  34 

limiting  voltage  of,  44 

(a.  c.)  limiting  voltage  of,  32 

(d.  c.)  limiting  voltage  of,  31 

overload  capacity,  103 

relation  between  voltage  and  capac- 
ity, 127 

revolving  armatures,  112 
fields,  112 

series-wound,  41 

speed  regulation,  38 
Glass  vs.  porcelain  insulators,  288 
Great  Falls  plant,  54,  60,  61,  64,  67,  78, 

92,  93,  102,  114,  118 
Greggs  Falls  plant,  54,  56,  64,  240 
Ground  connections,  178 

for  guard  wires,  171,  172 
Grounded  guard  wires,  168 
Guard  wires,  168 

installation  of,  175 
Guying  of  poles,  255 

HAGNECK  (Switzerland)  plant,  86 
Hooksett  Falls  plant,  56,  131 
Hydro-electric  plants,  i 

built  at  the  dam,  64-67 
canals,  long,  68-73 

long  and  short,  58 
short,  53-56 


330 


INDEX. 


Hydro-electric     plants,     capacity    and 
weight  of  conductors  per  k. 
w.  for  various  plants,  27 
(800  k.  w.)  cost  of,  10 
(1500  k.  w.)  cost  of,  ii 
cost  of  labor,  12 
cost  of  operation,  12,  77 
design  of,  83 
floor,  79 

space  per  k.  w.,  101 
interest  and  depreciation,  u 
linked  together,  56-58 
load  factors,  14,  15 
location  of,  64 
model  design,  12 
operation,  59 
vs.  steam  plant,  5,  12 
with  pipe-lines,  73-77 
with  steam  auxiliary,  84 

ICE,  59 

Impulse  wheel  speed,  108 

wheels,  82,  90 

location  of,  99 

Indian  Orchard  plant,  57,  84 
Inductance,  206,  230 
Induction,     electro-magnetic,     electro- 
static, 1 68 

on  lines,  206 

regulator,  162 
Inductor  alternators,  112 
Insulation,  as  affected  by  ozone,  197 

cost  of  paper  vs.  rubber,  196 

of  a.  c.  and  d.  c.  lines,  34 

of  apparatus,  142 

of  cables,  195 

of  electrical  machines,  45 

of  generators,  39 

protection  against  ozone,  198 
Insulator  arc -over  test,  291 

.-pins,  270  (see  Pins) 
Insulators,  277,  282,  287,  322 

and  pins,  data  from  various  plants, 
280 

defective,  288 

glass  vs.  porcelain,  288 

in  snow,  293 

method  of  fastening  to  iron  pins,  271 


Insulators,  novel  clamp,  323 

on  various  transmission  Hnes,  294 

petticoats,  294 

testing  of,  288 

tests,  290 

test  voltage,  289 

with  oil,  287 
Iron  conductors,  200 

KELLEY'S  FALLS  plant,  56 
Kelvin's  law,  219 

LABOR,  cost  of,  12 

in  hydro-electric  stations,  12 
Leakage,  275,  287 
line,  207,  214 
Lewiston  (Me.)  plant,   118,   120,   122, 

167,  213 

Lighting,  incandescent,  minimum  fre- 
quency, 116 
series  distribution,  167 
Lightning  arrester,  effect  of  series  re- 
sistance, 185 
arresters,  168,  176 

ground  connection,  178 
multiple  air-gap,  176,  183 
non-arcing  metals  in,  184 
series  connection  of,  180 
shunted  air-gaps,  185 
with  choke  coil,  180 
protection,  34 
Line  calculations,  221-232 
charging  current,  197 
conductors,  200 
conductors,  cost  of,  22 

weight  of,  21 
construction,  222 
cost,  310 
cross-arms,  49 
spacing  of  wires,  46 
(a.  c.)  transmission,  34 
(d.  c.)  transmission,  33 
end  strain,  325 
leakage,  47 
loss,  39 
losses  due  to  grounded  guard  wires, 

176 
Lines,  sag,  309 


INDEX. 


Lines,  transposition  of,  314 
Line  voltages,  45 
Load  factors,  14,  15 

lighting,  6 1 

maximum,  60 

motor,  1 60 

railway,  164 
Loss  in  conduits,  198 

relation  to  weight  of  conductors,  215 
Losses  due  to  grounded  guard  wire,  176 

on  transmission  lines,  215 
Ludlow  Mills  plant,  26,  27,  28,  57,  79, 
100,  121,  208^  213 

MADRID  (N.  M.)  plant,  26,  27,  28,  118, 

208 

Manchester  (N.  H.)  plants,  120 
Market  for  electric  power,  7 
Materials,  building,  95 

for  line-conductors,  200 
Mechanicsville  plant,  58,  67,  109,  121, 

174 

Melting  points  of  conductor  metals,  200 
Montmorency  Falls  plant,  26,  27,   28, 

240 

Motor  load,  160 

Motor-generator  set  efficiency  curve,  117 
Motors,  series- wound,  41 

(d.  c.)  speed  regulation,  38 
synchronous,  241 
Multiple  air-gap  arrester,  176 

NEEDLE-POINT  spark-gap  for  measuring 

pressure,  290 

Neversink  River  plant,  75,  179 
Niagara  Falls  Power  Co.,  3,  59,  81,  86, 

87>  93>  94,  95>  97>  IOI>  I02>  IO5>  Io6> 
107,  108,  112,  113,  117,  118,  119,  127, 

J33>  *?>*l,  MO,  i43,  !45>  I5I>  J53>  l6l> 
165,  170,  181,  188,  194,  195,  208,  211, 
240,  245,  246,  257,  272,  273,  275,  280, 
287,  289,  294,  295,  297 
Nitric  acid  from  air,  281 
Non-arcing  metals,  184 
North  Gorham  (Me.)  plant,  120 

Ogden  (Utah)  plant,  26,  27,  28,  118, 
120,  132,  134,  208,  245 


Ohm's  law,  223 
Oil  switches,  136 
Ontario  Power  Co.,  121 
Operating  expenses,  59 
Operation,  cost  of,  12,  77 
Operations,  reliability  of,  311 
Ouray  (Col.)  plant,  121 
Overhead   line   connection    to    under- 
ground, 197 

Overload  capacity  of  generators,  103 
Ozone,  197 

PAINTING  of  poles,  255 
Paper  insulated  cables,  196 

vs.  rubber  insulation,  196 
Payette  River  (Idaho)  plant,  73,  101 
Penstocks,  59,  98 
Phase,  113 

Pike's  Peak  plant,  77 
Pilot  wires,  161 
Pins,  259,  270 

and  insulators,  data  from  various 
plants,  280 

burning  of,  270,  276,  278 

charring  of,  276,  278 

composite,  281 

compressive  strength  of  woods,  302 

design  of,  298 

dimensions  of,  301 

formula  for  diameter  of,  299 

iron,  275,  285,  286 
expansion  of,  290 
method  of  fastening  insulators, 
271 

method  of  fastening  to  cross-arms, 
271 

metal,  271,  275,  282,  285,  286 

of  uniform  strength,  300,  302 

proportions,  301 

relative  cost  of  metal  and  wooden, 
284 

shank,  274 

shoulder,  275,  299,  305 

softening  of  threads,  280 

steel,  275,  312 

strain  with  $-inch  sleet  and  100- 
mile  wind  for  different  spans,  324 

strains  on,  270,  298 


332 


INDEX. 


Pins,  strength  of,  303 

table  of  standard,  301 

treatment  of,  259,  275 

weakest  point,  298 

wooden,  data  from  various  plants, 

272 

dimensions  of,  272 
dimensions  of  standard,  273 
Pipe-lines,  73 

Pittsfield  (Mass.)  plant,  121 
Pole  line,  cost  of,  21 

lightning  arresters,  179 
relative  cost  of,  20 
lines,  246 
Poles,  cost,  310 

depth  in  ground,  254 
diameter  of,  254 
dimensions  of,  254 
guying  of,  255 
iron,  284 

length  of,  253,  309 
life  of,  255 
setting  of,  252 
spacing  of,  249 
steel,  cost  of,  307 
treatment  of,  255 
woods  for,  252 

Porcelain  vs.  glass  insulators,  288 
Portland  (Me.)  plant,  120,  166,  239 
Portsmouth,  N.  H.  plant  (steam),  102, 
118,  119,  120,  121,  144,  194,  264,  294 
Power  plant,  relative  cost  of  a.  c.  and 

d.  c.,  36 
transmitted,  total  cost  of,  24 

RADIATION  loss  in  conduits,  198 
Railway  crossing,  187,  252 

service,  164 
Red  Bridge  plant,  53,  60,  79,  93,  94,  96, 

97,  99,  101,  102 
Regulation,  155,  239 

as  effected  by  synchronous  motors, 

165 

at  receiving  end,  162 
hand,  161 

Regulator,  automatic,  162 
constant-current,  167 
induction,  162 


Relay-switches,  145 
Resistance,  225 

in  series  with  lightning  arrester,  185 
Revolving  armature  alternators,  112 

field  alternator,  112 
River  crossings,  187,  190,  249 
Roof,  distance  from  floor,  95 
Roofs,  95 
Rope-drive,  83 
Rotaries,  cost  of,  117 

suitable  frequency  for,  115 
Rubber-covered  cables,  195 

maximum  temperature,  198 

protection  against  ozone,  198 

SAG  in  lines,  309 

St.  Hyacinthe  (Que.)  plant,  118 

St.  Joseph  plant,  66 

St.  Maurice  plant  (Switzerland),  31 

Salem  (N.  C.)  plant,  121,  122 

San  Gabriel  Canon  plant,  26,  27,  28,  208 

Santa  Ana  plant,  i,  26,  27,  28,  74,  76,  82, 

83,  92,  94,  95,  96,  97,  98,  99,  101,  102, 

208,  245,  263,  280,  281,  294,  295,  296 
Sault  Ste.  Marie  plant,  72,  83,  85,  89,  97, 

102,  104,  105,  112,  113,  117,  118,  120, 

127 

Scott  system,  132 
Series  distribution,  167 

machines,  41 

Sewall's  Falls  plant,  26,  27,  28,  155 
Shawinigan  Falls  plant,  i,  70,  71,  107, 

116,  117,  163,  164,  166,  209,  212,  213, 

235,  236,  242,  245,  267,  272,  273,  280, 

282,  294,  295,  296 
Sheaths  for  cables,  194 
Shunted  air-gaps,  185 
Skin  effect,  206,  232 
Snoqualmie  Falls  plant,  3,  4 

map  of  transmission  lines,  4 
Snow,  293 
Soldered  joints,  206 
Spacing  of  poles,  249 

of  wire,  234 
Spans,  long,  190,  250 

strains  for  different  lengths,  324 
Sparking  distances,  182 
voltages,  182 


INDEX. 


333 


Speed,  peripheral,  of  impulse  wheels,  108 
peripheral  of  turbines,  85,  103 
regulation,  38,  42 

d.  c.  motors,  38 

Spier  Falls  plant,  i,  2,  3,  54,  58,  61,  62, 
68,  91,  94,  98,  124,  126,  127,  130,  141, 
142,  146,  161,  174,  236,  237,  243,  244, 
245,  250,  253,  266,  280,  285,  287,  289, 
291,  294,  295,  296,  312 
Star  connection,  131 
Static  discharges,  170 
Steam  and  water-power  station    com- 
bined, 84 

electric  plant,  cost  of  labor,  12 
cost  of  operation,  12 
floor  area  per  k.  w.,  102 
vs.  water-power,  5 
Steel  towers,  306 
Storage  capacity,  15 
Strains  on  insulation  as  affected  by  re- 
sistance in  series  with  arrester,  185 
Stray  currents,  protection  against,  195 
Submarine  cables,  187,  192,  194 
Sub-station,  arrangement  of  apparatus, 

128 

Sub-stations,  157,  237 
Surges,  136 
Switchboard,  156 

wiring,  146,  148,  149 
Switches,  135,  244 
arcing  of,  135 
electrically  operated,  140 
long  break,  135 
oil,  136 
open-air,  136 

pneumatically  operated,  140 
power  operated,  138 
relay,  145 

Switch-houses,  141,  142,  2-38,  244 
Switching,  146 

high-tension,  147 
Synchronous  converters,  115 

cost,  117 
motors,  165,  241 

TAIL-RACE,  96 
Telephone,  161 
Telluride  plant,  47,  160,  169,  181 


Temperature  of  cables,  198 

rise  in  conduits,  198 
Tensile  strength  of  conductor  metals, 

201 

Time-limit  circuit-breaker,  152 
Time  relays,  152,  153 
Towers,  250,  306 

angle,  320 

cost,  310 

dimensions,  314 

erection  of,  316-319 

heavy,  320 

reliability  of  operation,  311 

spans,  313 

steel,  cost,  307,  308 

steel  pins,  312 

strain  on,  324 
Transformers,  122 

air-blast  vs.  water-cooled,  129 

artificially  cooled,  129 

at  sub-stations,  125 

blower  capacity  necessary  to  cool, 
130 

constant-current,  167 

cooling,   quantity  of  water  neces- 
sary, 129 

cost,  21,  116,  124,  134 

cost  of  operation,  129 

cost  of,  relative,  20 

delta  and  star  connections,  131 

efficiency,  133 

frequency,  effect  of,  116 

insulation,  45 

in  transmission  systems,  134 

limiting  voltage  for,  32 

location  of,  97 

polyphase,  124 

regulation,  125 

reserve,  149 

secondary,  in  series,  131 

single-phase,  124 

two-  to  three-phase,  132 

used  to  compensate  drop,  133 

used  to  regulate  voltage,  162 

voltages,  45 

when  to  use,  122 
Transmission,  constant-current,  38,  216 

constant-voltage,  40,  217 


334 


INDEX. 


Transmission,    continuous-current,   31, 

32 

control  equipment,  35 
cost  of,  19,  40,  222 
(d.  c.)  cost  of,  40 
efficiency,  35,  41 
first  long  line,  37 
frequency,  113 
generator  end,  103 
lightning  protection,  34 
limiting  voltage,  44 
lines,  arcing,  46 

calculation  of,  221-232 

charging  current,  197 

construction,  222 

cost,  310 

cross-arms,  49,  256 

crossings,  187,  190 

data  from  various  plants,  245 

effect  of  length  on  cost,  20 

effect    of    length    on    cost    of 
power,  24 

efficiency,  22,  24 

end  strain  at  entries,  325 

entrance  to  buildings,  179,  261 

inductance,  206 

induction,  168 

insulation,  34 

insulators  (see  Insulators),  287 

insulator-pins  (see  Pins),  270 

interest,  maintenance  and  de- 
preciation, 22 

leakage,  47,  207,  214 

length  of,  capacity  of,  popula- 
tion supplied,  8 

lightning  arresters  (see  Light- 
ning Arresters),  179 

lightning  protection,  118 

long  spans,  190 

loss,  22,  39 

losses,  215 

maximum  investment  in,  220 
;      method  of  fastening  conductors 
...    to  insulators,  323 

operation,  311 

pole  spacing,  249 

regulation    with    synchronous 
motors,  241 


Transmission  lines,  relative  weights  of 
three-phase,  two-phase,  and 
single-phase,  228 

right-of-way,  246 

sag  in,  309 

spacing  of  wire,  234 

steel  towers  (see  Towers), 
306 

switch-houses,  238 

switches,  fuses,  and  circuit- 
breakers,  135 

take     up,      arrangement     for, 

325 

total  cost  of,  22 

total  cost  of  operation,  23 

transposition  of  wires,  206, 
3i4 

voltage,  21,  215 
in  cables,  190 
regulation,  130 

wind  pressure,  210 
long  line,  221 
minimum-sized  wire,  202 
physical  limits  of,  44 
a.  c.  pole  line  construction,  34 
d.  c.  pole  line  construction,  33 
pole  lines,  246 
problems,  19 
regulation,  155,  239 
selection  of  circuits,  233 
single  vs.  parallel  circuits,  241 
spacing  of  conductors,  46 
submarine,  187 
three-phase,  113 
three-phase  and  two-phase,  228 
ewo-phase,  113 
underground,  187 
'  without  step-up  transformers,  120 
Transposition  of  wires,  206 
Turbines,  high-speed,  107 
horizontal,  79,  83,  89,  97 
impulse,  82,  90,  99 

speed  of,  108 
low-head  good  speed,  105 
peripheral,  speed  of,  85,  103 
pressure,  79 

several  on  same  shaft,  85,  105 
vertical,  79,  84,  85,  86,  97 


INDEX. 


335 


UNDERGROUND  cable  connected  to  over- 
head line,  197 
cables,  187 

VICTOR  (Colo.)  plant,  26,  27,  28,  208 
Virginia  City  plant,  118 
Voltage  drop  compensation,  133 

fluctuations,  218 

high,  alternators,  120 
measurements,  290 

in  cables,  190,  196 

limiting,  44 

for  a.  c.  machines,  32 
for  d.  c.  machines,  31 

of  transmission  lines,  21,  215 

regulation,  130,  155 

sparking,  182 

test  for  insulators,  289 
Volts  per  mile,  26 

WAGES  paid  attendants,  12 

Walls,  95 

Washington  &  Baltimore  Ry.,  121 

Washouts,  8r 

Water-cooled  transformers,  129 


Water-power,  development  of,  51 

high  head,  74-77 

low  head,  51-74 

per  cent,  of  energy  available,  16 

pure  hydraulic  development,  51 

stations  (see    Hydro-electric    Sta- 
tions) 

storage  capacity,  15,  6 1 

utilization  of,  10 

vs.  steam,  5 

Water,  storage  of,  15,  61 
Weight  of  the  conductor  metals,  202 
Welland  Canal  plant,  i,  26,  27,  28,  208, 

245,  248 

Westbrook  (Me.)  plant,  120 
White  River  to  Dales  plant,  26,  27,  28, 

7J>   134 

Wind,  324 

pressure  on  lines,  210 
Winooski  River  plant,  64 
Wire  room,  139 

Wood,  compressive  strength  of,  302 
Woods  for  poles,  252 
Yadkin  River  (N.  C.)  plant,  26,  27,  28, 
118,  208 


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